[IMP] website_event_sale:  'Validation of seats availability in cart'.

- Task: https://www.odoo.com/web?#id=9971&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.BTJ9yFYnbxBG3VzQ
Unnecessary variable assignation, you should directly check reg._check()[0].