task work change amount

[Milan Tribuson]

If you create a work by task and save it and try to edit that work and change the amount you get 'journal_id' error. This is because project_timesheet module has a write method that on project.task.work that will call timesheet_obj.on_change_unit_amount procedure with vals_line['journal_id'] which doesn't exist because 'user_id' doesn't exist in vals and you will get an error ('user_id' doesn't exist in vals because it stays the same).