LFS only checks stock amount while adding item to the cart

[pigletto]

It is possible that user puts items into the cart and, after hours/days, he proceeds to checkout. This can cause that items that are out of stock will be sold.

Fixed at my branch: https://github.com/pigletto/django-lfs/commit/f834e999db70d7645054fd2ff83fe6e00fc125b5

[pigletto]

fixed