fix(NSC): handle endpoint slice ready nil

[aauren]

@mrueg

In some cases it is possible for Endpoint.Conditions.Ready to be nil during the early stages of initialization. When this happens it causes kube-router to segfault. This fix tests for nil before testing for Ready.

Error looks like:

2023-12-08T19:26:16.577929290Z E1208 19:26:16.577532       1 runtime.go:79] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference)                                                                    
2023-12-08T19:26:16.577944838Z goroutine 257 [running]:                                                                                                                                                                                                                                 
2023-12-08T19:26:16.577949087Z k8s.io/apimachinery/pkg/util/runtime.logPanic({0x2d4e640, 0x45f71d0})                                                                                                                                                                                    
2023-12-08T19:26:16.577957166Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/runtime/runtime.go:75 +0x105                                                                                                                                                  
2023-12-08T19:26:16.577960142Z k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0x0})                                                                                                                                                                                        
2023-12-08T19:26:16.577964279Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/runtime/runtime.go:49 +0xbb                                                                                                                                                   
2023-12-08T19:26:16.577967687Z panic({0x2d4e640, 0x45f71d0})                                                                                                                                                                                                                            
2023-12-08T19:26:16.577971478Z  /home/shadowcat/sdk/go1.20.7/src/runtime/panic.go:890 +0x262                                                                                                                                                                                            
2023-12-08T19:26:16.577975270Z github.com/cloudnativelabs/kube-router/v2/pkg/controllers/proxy.(*NetworkServicesController).buildEndpointSliceInfo(0xc0004d43c0)                                                                                                                        
2023-12-08T19:26:16.577978699Z  /home/shadowcat/git-repos/kube-router/pkg/controllers/proxy/network_services_controller.go:1053 +0x4fb                                                                                                                                                  
2023-12-08T19:26:16.577982383Z github.com/cloudnativelabs/kube-router/v2/pkg/controllers/proxy.(*NetworkServicesController).OnEndpointsUpdate(0xc0004d43c0, 0xc001062000)                                                                                                               
2023-12-08T19:26:16.577985971Z  /home/shadowcat/git-repos/kube-router/pkg/controllers/proxy/network_services_controller.go:806 +0x688                                                                                                                                                   
2023-12-08T19:26:16.577989751Z github.com/cloudnativelabs/kube-router/v2/pkg/controllers/proxy.(*NetworkServicesController).handleEndpointSliceAdd(0xc0004d43c0, {0x3061b00, 0xc001062000})                                                                                             
2023-12-08T19:26:16.577992907Z  /home/shadowcat/git-repos/kube-router/pkg/controllers/proxy/network_services_controller.go:1780 +0xa6                                                                                                                                                   
2023-12-08T19:26:16.577996184Z github.com/cloudnativelabs/kube-router/v2/pkg/controllers/proxy.(*NetworkServicesController).newEndpointSliceEventHandler.func1({0x3061b00, 0xc001062000})                                                                                               
2023-12-08T19:26:16.577999770Z  /home/shadowcat/git-repos/kube-router/pkg/controllers/proxy/network_services_controller.go:1762 +0x36                                                                                                                                                   
2023-12-08T19:26:16.578003232Z k8s.io/client-go/tools/cache.ResourceEventHandlerFuncs.OnAdd({0xc0008fcd50, 0xc0008fcd60, 0xc0008fcd70}, {0x3061b00, 0xc001062000}, 0x0)                                                                                                                 
2023-12-08T19:26:16.578006524Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/tools/cache/controller.go:239 +0x50                                                                                                                                                       
2023-12-08T19:26:16.578009873Z k8s.io/client-go/tools/cache.(*processorListener).run.func1()                                                                                                                                                                                            
2023-12-08T19:26:16.578013183Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/tools/cache/shared_informer.go:974 +0x264                                                                                                                                                 
2023-12-08T19:26:16.578016541Z k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1(0xc0009a4f08)                                                                                                                                                                                       
2023-12-08T19:26:16.578020098Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/backoff.go:226 +0x3f                                                                                                                                                     
2023-12-08T19:26:16.578023524Z k8s.io/apimachinery/pkg/util/wait.BackoffUntil(0xc00056ff08, {0x35f5940, 0xc00077d950}, 0x1, 0xc0006f6900)                                                                                                                                               
2023-12-08T19:26:16.578026871Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/backoff.go:227 +0xc7                                                                                                                                                     
2023-12-08T19:26:16.578030174Z k8s.io/apimachinery/pkg/util/wait.JitterUntil(0xc0009a4f08, 0x3b9aca00, 0x0, 0x1, 0xc0006f6900)                                                                                                                                                          
2023-12-08T19:26:16.578033409Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/backoff.go:204 +0x85                                                                                                                                                     
2023-12-08T19:26:16.578036799Z k8s.io/apimachinery/pkg/util/wait.Until(0xc0009a4f08, 0x3b9aca00, 0xc0006f6900)                                                                                                                                                                          
2023-12-08T19:26:16.578040052Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/backoff.go:161 +0x33                                                                                                                                                     
2023-12-08T19:26:16.578043306Z k8s.io/client-go/tools/cache.(*processorListener).run(0xc000958750)                                                                                                                                                                                      
2023-12-08T19:26:16.578046528Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/tools/cache/shared_informer.go:968 +0x7a                                                                                                                                                  
2023-12-08T19:26:16.578049920Z k8s.io/apimachinery/pkg/util/wait.(*Group).Start.func1()                                                                                                                                                                                                 
2023-12-08T19:26:16.578053604Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/wait.go:72 +0x90                                                                                                                                                         
2023-12-08T19:26:16.578057104Z created by k8s.io/apimachinery/pkg/util/wait.(*Group).Start                                                                                                                                                                                              
2023-12-08T19:26:16.578064118Z  /home/shadowcat/go-workspace/pkg/mod/k8s.io/[email protected]/pkg/util/wait/wait.go:70 +0xb1                                                                                                                                                         
2023-12-08T19:26:16.583308299Z panic: runtime error: invalid memory address or nil pointer dereference [recovered]                                                                                                                                                                      
2023-12-08T19:26:16.583322624Z  panic: runtime error: invalid memory address or nil pointer dereference                                                                                                                                                                                 
2023-12-08T19:26:16.583326297Z [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x23bfd5b]