Minor - avoid custom code, use findUserByUsername.

Author: jmontoyaa

main/inc/lib/webservices/WebService.class.php

@@ -1,5 +1,6 @@
 <?php
 /* For licensing terms, see /license.txt */
+
 use Chamilo\UserBundle\Entity\User;
 
 /**
@@ -77,8 +78,7 @@ public static function isValidUser($username, $password)
             return false;
         }
 
-        /** @var \Chamilo\UserBundle\Entity\User $user */
-        $user = UserManager::getRepository()->findOneBy(['username' => $username]);
+        $user = UserManager::getManager()->findUserByUsername($username);
 
         if (!$user) {
             return false;