Original PR description

If a department & an employee are set on a maintenance request, we select an equipment linked to the department *or* the employee **or no employee at all** (regardless of the department).

Removed the last clause. It does remove the ability to select an employee and then select an equipment linked to the employee or no employee at all, but I think it makes somewhat more sense than being able to select any equipment not linked to an employee when setting both employee and department.

ping @oma-odoo 

Also technically we might want a helper to apply a field's domain on a record somehow: onchange_department_or_employee_id has to pretty much duplicate the domain do do its thing, and it's likely bugged given the domain it defines (see above).