Fix errors caused by multi-target messages sent from LAN host (#4536)

src/main/java/net/minecraftforge/fml/common/network/FMLOutboundHandler.java

@@ -304,8 +304,10 @@ public class FMLOutboundHandler extends ChannelOutboundHandlerAdapter {
         }
         for (NetworkDispatcher targetDispatcher : dispatchers)
         {
-            targetDispatcher.sendProxy((FMLProxyPacket) msg);
+            pkt.payload().retain();
+            targetDispatcher.sendProxy(pkt);
         }
+        pkt.payload().release();
     }
 
 }