[FIX] account: raise warning when inv amount falls bellow 0
[FIX] account: raise warning when inv amount falls bellow 0

A warning was raised when an invoice line had a negative amount that may cause some
trouble when dealing with discount (negative amount). Now, the warning is raised
when the amount total of the invoice falls bellow 0.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo