Fix cart crash on spamming swap and remove

Crash happened when user was spamming enter and tab - switching over move and remove buttons through different rows in cart when multiple operations were added. This lead to situation when remove of last item was clicked (row was still visible), user tabbed and clicked move down button of upper row (it still wasn't disabled), so finally move mechanism tried to move item to index which was out of range of cart.

Changes by @mzebrak