[FIX] mrp: suggest the qty to produce instead of 0 in workorders

Before this commit, if any workorder is stared to produce, qty
producing was 0. After this commit, if product tracking is none
then system will suggest the remaining qty of workorder to produce
when user is start it.

TaskId - 2480775

closes odoo/odoo#70153

Related: odoo/enterprise#18063
Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>