Fixing ACL Listing for Cursors

I'm getting the following error when using ACLs via Mongo and going to the edit ACLs screen:

> Catchable fatal error: Argument 3 passed to Sonata\AdminBundle\Util\AdminObjectAclData::__construct() must be of the type array, object given, called in ~/Sonata/AdminBundle/Controller/CRUDController.php on line 787 and defined in ~/Sonata/AdminBundle/Util/AdminObjectAclData.php on line 79

This PR will fix that by seeing that aclUsers is an object and convert it to an expected array.