load authentication apps before checking wether user exists. fixes oc-910

lib/user.php

@@ -242,12 +242,13 @@ class OC_User {
 	 * Checks if the user is logged in
 	 */
 	public static function isLoggedIn(){
-		if( isset($_SESSION['user_id']) AND $_SESSION['user_id'] AND self::userExists($_SESSION['user_id']) ){
+		if( isset($_SESSION['user_id']) AND $_SESSION['user_id']) {
+			OC_App::loadApps(array('authentication'));
+			if (self::userExists($_SESSION['user_id']) ){
 				return true;
 			}
-		else{
-			return false;
 		}
+		return false;
 	}
 
 	/**