修复参数为ByteBuf造成的ClassCastException

src/main/java/io/github/yezhihao/netmc/codec/MessageEncoderWrapper.java

@@ -31,6 +31,9 @@ public class MessageEncoderWrapper extends ChannelOutboundHandlerAdapter {
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
         ByteBuf buf = null;
         try {
+            if (msg instanceof ByteBuf)
+                buf = (ByteBuf) msg;
+            else
                 buf = encoder.encode(msg);
             if (log.isInfoEnabled())
                 log.info("<<<<<原始报文[ip={}],hex={}", ctx.channel().remoteAddress(), ByteBufUtil.hexDump(buf));