Fix Locale Listener quand on se connecte en superadmin (memory user)

(cherry picked from commit fde6f4c8f161c105ffa906da79e88715b36b0502)

src/EventSubscriber/UserLocaleSubscriber.php

@@ -2,6 +2,7 @@
 
 namespace App\EventSubscriber;
 
+use App\Entity\User;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\HttpFoundation\RequestStack;
 use Symfony\Component\Security\Http\Event\InteractiveLoginEvent;
@@ -24,7 +25,7 @@ class UserLocaleSubscriber implements EventSubscriberInterface
     {
         $user = $event->getAuthenticationToken()->getUser();
 
-        if (null !== $user->getAppLanguage()) {
+        if ($user instanceof User && null !== $user->getAppLanguage()) {
             $this->requestStack->getSession()->set('_locale', $user->getAppLanguage());
         }
     }