ensure a session is available when displaying courseware public links, fixes #4351

Closes #4351

Merge request studip/studip!3152

app/controllers/courseware/public.php

@@ -4,6 +4,8 @@ use Courseware\PublicLink;
 
 class Courseware_PublicController extends StudipController
 {
+    protected $with_session = true;
+
     public function before_filter(&$action, &$args)
     {
         parent::before_filter($action, $args);