PHP FATAL error with AJAX routine for get_group_members.php

[hakasapl]

Issue reported by Kevin in AJAX routine.

PHP Fatal error:  Uncaught Error: Call to a member function getFirstname() on array in /srv/www/unity-web-1.1.1/webroot/admin/ajax/get_group_members.php:57\nStack trace:\n#0 {main}\n  thrown in /srv/www/unity-web-1.1.1/webroot/admin/ajax/get_group_members.php on line 57