Member list sorting was failing at recognizing sortable columns - tha…

…nks Inter for reporting - fixes #2010

Signed-off-by: emanuele <emanuele45@gmail.com>

sources/controllers/Memberlist.controller.php

@@ -238,7 +238,7 @@ public function action_mlall()
 			$context['num_members'] = ml_memberCount();
 
 		// Set defaults for sort (real_name) and start. (0)
-		if (!isset($_REQUEST['sort']) || !isset($context['columns'][$_REQUEST['sort']]))
+		if (!isset($_REQUEST['sort']) || !isset($context['columns'][$_REQUEST['sort']]['sort']))
 			$_REQUEST['sort'] = 'real_name';
 
 		if (!is_numeric($_REQUEST['start']))