[FIX]sale_stock: do not raise if not able to find any warehouse (for the get...

[FIX]sale_stock: do not raise if not able to find any warehouse (for the get default warehouse), it can prevent the user of doing anything (if he does an upgrade of sale_stock module while having no warehouse set, the user will not be able to sign in in his instance again).

bzr revid: dle@openerp.com-20131203095544-i5vmow007dgjbiza