Fix error when retrieving FCM token after updating to FCM 10.23

The first time the app starts it works fine, but after restarting the app the code calls initRegistration too soon and it fails.

src/ios/PushPlugin.m

@@ -381,6 +381,9 @@ - (void)didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken {
 
         if(![weakSelf usesFCM]) {
             [weakSelf registerWithToken: token];
+        } else {
+            // Obtain the FCM token now that the APNS token is available, otherwise initRegistation fails.
+            [weakSelf initRegistration];
         }
     }];