Manage My Identity throws errors

For some but not all COUs (not sure what the difference is) selecting "Manage My <CO> Identity" throws errors because Model/Cou/childCous gets a non-array when calling $this->children. Subsequently, array_merge throws another error because $allChildren is NULL.

In addition to fixing whatever the underlying cause is, better error checking should be added to prevent a PHP error from being thrown.

This may be related to CO-230.