get_working_duration can't work on generated samples. closes odoo/odoo#107934 Task: 3098709 X-original-commit: 642ca37e4e5a3db6ef7929a25850fafc499e4257 Signed-off-by: William Henrotin (whe) <whe@odoo.com> Signed-off-by: Jean-François Aubert <ajf@odoo.com>