Quiz with sequential navigation doesn't work properly

As reported in MOBILE-4345, MDL-75210 caused a regression with quizzes using sequential navigation.

In particular, the following condition was introduced in mod/quiz/classes/external.php :

if ($attemptobj->check_page_access($attemptobj->get_question_page($slot), false)) {

    $questions[] = $question;

}

This prevents the app from getting information about any question that is not the current, and thus prevents the bookmarks and quiz summary/review from displaying properly. It also affected navigation itself, but a workaround to fix that was introduced in MOBILE-4345 (it should be reverted once a proper solution is introduced).