[Linux DS 64] file.AsyncRead isn't Async

[RaphaelIT7]

Details

On Linux 64x file.AsyncRead doesn't seem to be Async.

My guess is that the filesystem's threadpool isn't started properly / same issue as #5310 but I didn't verify this yet.
https://github.com/perilouswithadollarsign/cstrike15_src/blob/master/filesystem/filesystem_async.cpp#L639

Steps to reproduce

1. Start a Linux DS Server
2. Run lua_run local a=SysTime() for k=1, 50 do file.AsyncRead("steamclient.so", "BASE_PATH", function() end) end print(SysTime()-a)
3. Watch it freeze the main thread

[RaphaelIT7]

Just verified it and it really seems like bEnableOnLinuxDedicatedServer is missing for the threadpool.