Clone FML packet indexes if channel is not open. Fixes potential threading issue.

src/main/java/net/minecraftforge/fml/common/network/handshake/NetworkDispatcher.java

@@ -238,7 +238,7 @@ public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> imple
             manager.closeChannel(new ChatComponentText("Handshake Complete review log file for details."));
         scm.initializeConnectionToPlayer(manager, player, serverHandler);
     }
-    
+
     @Override
     protected void channelRead0(ChannelHandlerContext ctx, Packet msg) throws Exception
     {
@@ -430,6 +430,8 @@ public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> imple
 
     public void sendProxy(FMLProxyPacket msg)
     {
+        if (!manager.isChannelOpen())
+            msg = msg.copy();
         manager.sendPacket(msg);
     }
 

src/main/java/net/minecraftforge/fml/common/network/internal/FMLProxyPacket.java

@@ -186,4 +186,13 @@ public class FMLProxyPacket implements Packet<INetHandler> {
     {
         return target;
     }
+
+    public FMLProxyPacket copy()
+    {
+        FMLProxyPacket pkt = new FMLProxyPacket(new PacketBuffer(payload.duplicate()), channel);
+        pkt.dispatcher = dispatcher;
+        pkt.netHandler = netHandler;
+        pkt.target = target;
+        return pkt;
+    }
 }