[FIX] website: unpublished page present in menu throws an error if public user

Before this commit, an unpublished page present in menu would throw an error for
public user (group_portal & group_public) because of the security record rule
set on website.page model not allowing read access to unpublished pages:

<field name="domain_force">[('website_published', '=', True)]</field>

In this particular case, we try to retrieve the menu URL, but since the URL is
retrieved through its (m2o) website.page, it would cause an error.

Now, it the menu has a website.page unpublished, we will correctly retrieve its
URL (sudo) and it won't crash.

addons/website/models/website.py

@@ -705,7 +705,7 @@ class Menu(models.Model):
     def clean_url(self):
         # clean the url with heuristic
         if self.page_id:
-            url = self.page_id.url
+            url = self.page_id.sudo().url
         else:
             url = self.url
             if not self.url.startswith('/'):