Fixed #26085 -- Fixed contenttypes shortcut() view crash with a null fk to Site.

Thanks Fabien Schwob for the initial patch.

django/contrib/contenttypes/views.py

@@ -63,9 +63,11 @@ def shortcut(request, content_type_id, object_id):
             for field in obj._meta.fields:
                 if field.remote_field and field.remote_field.model is Site:
                     try:
-                        object_domain = getattr(obj, field.name).domain
+                        site = getattr(obj, field.name)
                     except Site.DoesNotExist:
-                        pass
+                        continue
+                    if site is not None:
+                        object_domain = site.domain
                     if object_domain is not None:
                         break