Error on profile adding contact to non-public group

When a profile form is submitted that adds a contact to a non-public group, this error is returned:
warning: implode() [function.implode]: Invalid arguments passed in .../sites/all/modules/civicrm/CRM/Mailing/Event/BAO/Subscribe.php on line 375.

Some debugging shows that the subscribe() function there returns null in the case that the group's visibility is not public (line 75). In that case, the group is added to the array of failed group add attempts, but the success flag is still marked as true, causing the error in trying to form the notification message.

I've attached a patch changing line 369 to read
$success = false;
as it had before the fix in response to CRM-6542. There may have been some rationale for that, however--I don't know.