Chunk Cache Center + small bug fix

I have made it so the server will finally send the SetChunkCacheCenter packet whenever you move, just like the vanilla server. Previously this was only send on login, and seemingly stalled my server for no reason when I tried to send it continuously.
I found out that the issue was in my WriteVarInt function, where negative values lead to an infinite loop. Now that this is fixed I can send that packet anytime now!!