[FIX] website: prevent crash when 'force_website_id' has been deleted

As an admin or website publisher, you have the possibility to switch website in
the navbar. This will force a website in your session*.

If this website is removed at some point, your session will be broken as the
dispatch will lead to a traceback, trying to read un unexisting website.

* There is other way to have the website forced in the session: theme install,
  go to website from settings, create website from settings..

opw-2092845

X-original-commit: 835d1201

addons/website/models/website.py

@@ -519,7 +519,12 @@ class Website(models.Model):
     @api.model
     def get_current_website(self, fallback=True):
         if request and request.session.get('force_website_id'):
-            return self.browse(request.session['force_website_id'])
+            website_id = self.browse(request.session['force_website_id']).exists()
+            if not website_id:
+                # Don't crash is session website got deleted
+                request.session.pop('force_website_id')
+            else:
+                return website_id
 
         website_id = self.env.context.get('website_id')
         if website_id: