MDL-55398 mod_feedback: prevent direct script access to lib files.

mod/feedback/lib.php

@@ -23,6 +23,8 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+defined('MOODLE_INTERNAL') || die();
+
 /** Include eventslib.php */
 require_once($CFG->libdir.'/eventslib.php');
 // Include forms lib.