Fix `[[textdownload]]` again. Should now work with quizzes, btu will really...

Fix `[[textdownload]]` again. Should now work with quizzes, btu will really need some help from Tim to figure out how to check whether the active user is the user that made the attempt.

Should help with #933.

textdownload.php

@@ -59,7 +59,16 @@ $qa = $dm->load_question_attempt($qaid);
 $question = $qa->get_question();
 $question->apply_attempt_state($qa->get_step(0));
 
-if (!stack_user_can_view_question($question)) {
+// We have a slight problem accessing the user connected to that attempt and
+// therefore this will only work with `quiz` type activities for now.
+$params = [$qa->get_usage_id(), 'mod_quiz'];
+$tmp = $DB->get_record_sql('SELECT qas.userid FROM {quiz_attempts} qas, {question_usages} qu WHERE qu.id = ? AND qu.component = ? AND qu.id = qas.uniqueid;', $params, IGNORE_MISSING);
+$usageuser = -1;
+if ($tmp !== false) {
+    $usageuser = $tmp->userid;
+}
+
+if (!(stack_user_can_view_question($question) || $USER->id === $usageuser)) {
     header('HTTP/1.0 403 Forbidden');
     header('Content-Type: text/plain;charset=UTF-8');
     echo 'This question is not accessible for the active user';