Fix uninitialized array causing php warning (#6046)

When $res->fetch() brings nothing, $listName is undefined and generates this warning :
PHP Warning:  in_array() expects parameter 2 to be array, null given in /usr/share/centreon/www/class/centreon-clapi/centreonCentbrokerCfg.class.php on line 411
So I suggest to initialize it as an empty array before.