Core/AH: Fix memory leak

Fix memory leak in Auction House when creating an auction with stackable items and a stack of the same amount in the inventory. Leak added in 15a2acfb52 .

src/server/game/Handlers/AuctionHouseHandler.cpp

@@ -332,6 +332,7 @@ void WorldSession::HandleAuctionSellItem(WorldPacket& recvData)
                 item2->DeleteFromInventoryDB(trans);
                 item2->DeleteFromDB(trans);
                 CharacterDatabase.CommitTransaction(trans);
+                delete item2;
             }
             else // Item stack count is bigger than required count, update item stack count and save to database - cloned item will be used for auction
             {