Fix entity spawn messages not handling buffer correctly (#4524)

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

@@ -60,7 +60,9 @@ public class EntitySpawnHandler extends SimpleChannelInboundHandler<FMLMessage.E
     {
         if (msg.getClass().equals(FMLMessage.EntitySpawnMessage.class))
         {
-            spawnEntity((FMLMessage.EntitySpawnMessage)msg);
+            FMLMessage.EntitySpawnMessage spawnMsg = (FMLMessage.EntitySpawnMessage) msg;
+            spawnEntity(spawnMsg);
+            spawnMsg.dataStream.release();
         }
     }
 

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

@@ -244,7 +244,7 @@ public abstract class FMLMessage {
                 speedScaledY = dat.readInt() / 8000D;
                 speedScaledZ = dat.readInt() / 8000D;
             }
-            this.dataStream = dat;
+            this.dataStream = dat.retain();
         }
     }
     abstract void toBytes(ByteBuf buf);