[#1714] Make a copy of the main Minecraft buffer as EntityMap.rewriteVarInt may require more bytes than available.

protocol/src/main/java/net/md_5/bungee/protocol/MinecraftDecoder.java

@@ -21,7 +21,7 @@ public class MinecraftDecoder extends MessageToMessageDecoder<ByteBuf>
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception
     {
         Protocol.DirectionData prot = ( server ) ? protocol.TO_SERVER : protocol.TO_CLIENT;
-        ByteBuf slice = in.slice().retain();
+        ByteBuf slice = in.copy(); // Can't slice this one due to EntityMap :(
 
         try
         {