fixes #284, fix regression

lib/models/resources/ResourceRequest.class.php

@@ -1198,10 +1198,13 @@ class ResourceRequest extends SimpleORMap implements PrivacyObject, Studip\Calen
         $intervals = $this->getTimeIntervals(false, true);
         foreach ($intervals as $interval) {
             $room = '';
+
+            if ($interval['range'] == 'CourseDate') {
                 $date = call_user_func([$interval['range'], 'find'], $interval['range_id']);
                 if ($room_obj = Room::find($date->room_booking->resource_id)) {
                     $room = $room_obj->name;
                 }
+            }
 
             $same_day = (date('Ymd', $interval['begin'])
                 == date('Ymd', $interval['end'])