MDL-42640 quiz: Fix restore of backup without overduehandling setting

Use default quiz overduehandling setting when restoring a
backup from older Moodle version that does not have a quiz
overduehandling setting.

mod/quiz/backup/moodle2/restore_quiz_stepslib.php

@@ -220,6 +220,10 @@ protected function process_quiz($data) {
             unset($data->popup);
         }
 
+        if (!isset($data->overduehandling)) {
+            $data->overduehandling = get_config('quiz', 'overduehandling');
+        }
+
         // Insert the quiz record.
         $newitemid = $DB->insert_record('quiz', $data);
         // Immediately after inserting "activity" record, call this.