uc_multi_stock error when order is not nicely ended

Hi,
See: http://www.ubercart.org/issue/13104/impossible_complete_order
When something comes between the orderhandling, a user clicks back or someting like that, I got this foreach error as explained in this Ubercart issue.

Invalid argument supplied for foreach() in the file sites/all/modules/uc_multi_stock/uc_multi_stock.module in line 122.

It has something to to with (order review and order complete, seems to clear $_SESSION['cart_order'] ), but I am not a good enough programmer to figure out what goes wrong.

Thanks a lot in advance for your reply!
greetings, Martijn