Spigot patch update: 0006 Async Operation Catching

Catch and throw an exception when a potentially unsafe operation occurs on a thread other than the main server thread.

https://github.com/EcoCityCraft/Spigot/blob/d9c76252eb02f7d0d6bea11efe77e3bb1edb0d99/CraftBukkit-Patches/0006-Async-Operation-Catching.patch