bug #1179

if there's a delivery date (date_livraison) then use it instead of the validation date (date_valid) to check if we need to display a warning or not...

For example, if we are in Septembre and there's an order that was validated in june but its delivery date is set to november then a warning is not necessary, since there's nothing to do but wait for the order to be delivered.

see https://doliforge.org/tracker/?func=detail&aid=1179&group_id=144