Prevent FindNextOpenClientSlot from returning duplicate IDs if called…

[tylerjwatson]

… simultaneously in a multi-thread scenario.

This places a more granular locks in the FindNextOpenClientSlot method, effectively preventing it from returning duplicate IDs if ever called in parallel. It's the same fix as #108 but not locking against network I/O which is a good candidate for deadlocks.

I am going to need testing.

[hakusaro]

As a result of the mintaka changes, this has been obsoleted. @DeathCradle do we need to work on implementing this as a modification?

[SignatureBeef]

@nicatronTg There are two ways of doing this:

1. Use the existing Hooks.Net.Socket.Accepted OTAPI hook to reimplement Netplay.OnConnectionAccepted and use additional changes proposed here.
2. A new TShock.Modification to reimplement Netplay.FindNextOpenClientSlot with these changes

Pro/con's for 1:

• Pro. Should only require ~10 extra lines of code
• Pro. No need to work with the OTAPI patcher - so other devs can fix or implement this
• Con. The extra lines of code will need to be kept in sync with Terraria's changes

Pro/con's for 2:

• Pro. Shouldn't change often/need to be kept in sync with Terraria's changes
• Con. A new project, so more changes overall
• Con. Less people know how modifications work

Either way is simple for me, let me know which you prefer.

[hakusaro]

Well 2 pros on 1 and 1 on 2 means that 1 wins. Go with 1 c:

[SignatureBeef]

Closing off as @tylerjwatson's changes have already been ported into Mintaka some time ago now.
See https://github.com/NyxStudios/TerrariaAPI-Server/blob/general-devel/TerrariaServerAPI/TerrariaApi.Server/Hooking/NetHooks.cs#L140