Core/Items: Fix disenchant/refund exploit

Fix exploit that allowed to refund an item after disenchanting it.
Closes #11227

src/server/game/Handlers/ItemHandler.cpp

@@ -1443,6 +1443,10 @@ void WorldSession::HandleItemRefund(WorldPacket &recvData)
         return;
     }
 
+    // Don't try to refund item currently being disenchanted
+    if (_player->GetLootGUID() == guid)
+        return;
+
     GetPlayer()->RefundItem(item);
 }