[FIX] mrp: fix change MO qty to produce

Before this commit, if a user changes a MO move qty to 0
and then tries to change the MO qty to produce, an error occurs.

The move with 0 qty is no longer cancelled or unlinked as this was not
the intenteded behavior.

Since the change production wizard no longer deletes cancelled moves
a test was updated accordingly.

closes odoo/odoo#107821

Taskid: 3082611
Signed-off-by: Arnold Moyaux (arm) <arm@odoo.com>