[FIX] sale: set timesheet line to zero
[FIX] sale: set timesheet line to zero

- Create a SO with a product that is a service and will be invoiced
  based in delivery quantities and will be tracked on timesheets and
  contract.
- Confirm
- Use a simple user that only has for rights: "Employee"
- Create a timesheet as the employee for the contract created by the sale
- Log some time
- Save it
- Check the SO: ok the number of hours should be "to be invoiced"
- Edit the timesheet and set one day to 0 hours => Access Error

In case of a zero value, the timesheet widget sends an unlink command
for the corresponding entry. In this case, the `sudo` is not set at the
appropropriate moment since the context key `force_so_lines` will resue
lines which are not defined in the `sudo` environment.

opw-728453

Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,bplancher/odoo,hip-odoo/odoo,ygol/odoo,Elico-Corp/odoo_OCB,ygol/odoo,bplancher/odoo,hip-odoo/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,bplancher/odoo,ygol/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,bplancher/odoo,hip-odoo/odoo,Elico-Corp/odoo_OCB,ygol/odoo,ygol/odoo