[FIX] calendar: all day event

- Go to the calendar list view
- Click on 'Create'
- Tick 'All Day'
- Set a start date

The end date is set to the day before.

This happens because in this case, the default duration is zero.

opw-2236766

closes odoo/odoo#49670

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>