[FIX] website_event: Impossible to track proposal on website

Programming error introduced by 602807acdf

Steps to reproduce the bug:

- Create an event with category='conference'
- Checked Track Proposals on Website
- Save it

An error was raised saying that the website with the id of the event didn't exist.

Further, with the fix but without a website_id specified, checked Track proposal didn't
add the menu to track proposals on the conference.

opw:1904078

closes odoo/odoo#28688

addons/website_event/models/event.py

@@ -81,7 +81,7 @@ class Event(models.Model):
                     event.menu_id.unlink()
                 elif event.website_menu:
                     if not event.menu_id:
-                        root_menu = self.env['website.menu'].create({'name': event.name, 'website_id': event.id})
+                        root_menu = self.env['website.menu'].create({'name': event.name, 'website_id': event.website_id.id})
                         event.menu_id = root_menu
                     for sequence, (name, url, xml_id) in enumerate(event._get_menu_entries()):
                         event._create_menu(sequence, name, url, xml_id)
@@ -96,7 +96,7 @@ class Event(models.Model):
             'url': url,
             'parent_id': self.menu_id.id,
             'sequence': sequence,
-            'website_id': self.id,
+            'website_id': self.website_id.id,
         })
         return menu
 

addons/website_event/views/event_views.xml

@@ -31,7 +31,7 @@
         <field name="inherit_id" ref="event.view_event_form"/>
         <field name="arch" type="xml">
             <field name="organizer_id" position="before">
-                <field name="website_id" options="{'no_create': True}" groups="website.group_multi_website"/>
+                <field name="website_id" options="{'no_create': True}"  attrs="{'required': [('website_menu','=',True)]}" groups="website.group_multi_website"/>
             </field>
             <button name="toggle_active" position="before">
                 <field name="website_url" invisible="1"/>