Bug 35514: Fix total cost update when adding multiple items to order

Bug 35514: Fix total cost update when adding multiple items to order

Test plan:

1) Create a basket and add an order line to go on neworderempty.pl
   (the new order form)
2) Choose to add one item and repeat the operation
3) See on form that the total cost is updated without update vendor
   price
4) Now add multiple items, for example, "2" you will see that the total
   cost is not updated
5) Apply this patch, refresh form and repeat steps 3 to 5

Signed-off-by: Michał Dudzik <dudzikmichal@wp.pl>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>