[IMP] website_sale, purchase: fix condition on portal_customer existence

Small correction to make the code more robust.

Technical note: we encountered a case where the group 'portal_customer' (to
classify recipient for mail_thread) where not present although it is added by
portal.mixin inherited by sale.order. That problem has been fixed since. So it
doesn't fix an actual problem but a potential one (condition of the "if" cannot
be false because the generator will generate an exception before).

Task-2674649

Part-of: odoo/odoo#103966

addons/website_sale/models/sale_order.py

@@ -410,7 +410,7 @@ class SaleOrder(models.Model):
             return groups
 
         self.ensure_one()
-        customer_portal_group = next(group for group in groups if group[0] == 'portal_customer')
+        customer_portal_group = next((group for group in groups if group[0] == 'portal_customer'), None)
         if customer_portal_group:
             access_opt = customer_portal_group[2].setdefault('button_access', {})
             if self._context.get('website_sale_send_recovery_email'):