Fixes #141 fatal error caused by new groups tidy

take.php

@@ -50,7 +50,7 @@ $pageparams->group = groups_get_activity_group($cm, true);
 $pageparams->init($course->id);
 $att = new attendance($att, $cm, $course, $PAGE->context, $pageparams);
 
-$allowedgroups = groups_get_activity_allowed_groups($this->cm);
+$allowedgroups = groups_get_activity_allowed_groups($cm);
 if (!empty($pageparams->grouptype) && !array_key_exists($groupid, $allowedgroups)) {
      $group = groups_get_group($pageparams->grouptype);
      throw new moodle_exception('cannottakeforgroup', 'attendance', '', $group->name);