[FIX] sale_timesheet: fix task creation when no tasks

Create a sale order with a service configured with
- Service Invoicing Policy: Timesheets on tasks
- Service Tracking: Create a new project but no task
Save and confirm. Access the project and the tasks via smart button.
Create a new task.

The task will not be saved under the current project because there is no
data reference in context.

opw-2355547

closes odoo/odoo#60690

X-original-commit: 51ce1d6ca479b4d851eacef70212bf890588e1c7
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>
Signed-off-by: agr-odoo <agr-odoo@users.noreply.github.com>