Notice how the $grader variable is defined twice in a row in the "quiz_get_recent_mod_activity" function:

$context = get_context_instance(CONTEXT_MODULE, $cm->id);
$grader = has_capability('moodle/grade:viewall', $context);
$accessallgroups = has_capability('moodle/site:accessallgroups', $context);
$viewfullnames = has_capability('moodle/site:viewfullnames', $context);
$grader = has_capability('mod/quiz:grade', $context);
$groupmode = groups_get_activity_groupmode($cm, $course);

I'm assuming the second one is correct, meaning the first could simply be deleted.