Handle null episode in check event acl

Users have no permissions on videos added from the work place. This patch fixes this problem by fetching the episode from opencast if the `$episode` parameter is null.

lib/Models/Videos.php

@@ -886,6 +886,12 @@ class Videos extends UPMap
      */
     public static function checkEventACL($eventType, $episode, $video)
     {
+        // Fetch episode if null
+        if (empty($episode)) {
+            $api_client  = ApiEventsClient::getInstance($video->config_id);
+            $episode = $api_client->getEpisode($video->episode);
+        }
+
         // Only allow updating of metadata if event has publications
         if (!Helpers::canEventRunWorkflow($episode, $video)) {
             return;