Prevent adding to administratror group when Drupal author is anonymous

When the civicrm_og_sync is triggered, the author of the group (as owner) is added to a corresponding CiviCRM group : adminsitrator'. However, this fails when the author is anonymous.

Solution would be to check whether the uid is anon and prevent the call to the bridge to populate.
Workaround is to change the author in Drupal, e.g. to admin.