Fix "AnonymousUser has no attribute 'email'" errors when not logged in

We shouldn't be looking for this attribute unless the user has logged in
- this was a regression in the recent email case fix.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

layerindex/models.py

@@ -76,8 +76,8 @@ class LayerItem(models.Model):
         return matches
 
     def user_can_edit(self, user):
-        user_email = user.email.strip().lower()
         if user.is_authenticated():
+            user_email = user.email.strip().lower()
             for maintainer in self.active_maintainers():
                 if maintainer.email.strip().lower() == user_email:
                     return True