I think this should work:
// Is this a moved topic that we are redirecting to?
if (!empty($topicinfo['id_redirect_topic']))
{
markTopicsRead(array($user_info['id'], $topic, $topicinfo['id_last_msg']), $topicinfo['new_from'] !== 0);
redirectexit('topic=' . $topicinfo['id_redirect_topic'] . '.0');
}
in Display.php about line 133