Currently when a time off using an overtime is written to for any
reason, it will compare the duration of the overtime with the
number_of_hours_display. However, the duration check will always be
triggered since overtime duration is number_of_hours_display * -1
This causes problems if an overtime time off is modified for any reason
and the employee does not have enough total_overtime
closesodoo/odoo#160381
X-original-commit: 1c477259d08995d1b0bfe8ebd551452073e0c03b
Signed-off-by: Sofie Gvaladze (sgv) <sgv@odoo.com>