MDL-30646 default qbank sort should only use visible columns.

mod/quiz/editlib.php

@@ -1106,6 +1106,10 @@ class quiz_question_bank_view extends question_bank_view {
                 'editaction', 'previewaction');
     }
 
+    protected function default_sort() {
+        return array('qtype' => 1, 'questionnametext' => 1);
+    }
+
     /**
      * Let the question bank display know whether the quiz has been attempted,
      * hence whether some bits of UI, like the add this question to the quiz icon,

question/editlib.php

@@ -965,7 +965,7 @@ class question_bank_view {
     }
 
     /**
-     * Deal with a sort name of the forum columnname, or colname_subsort by
+     * Deal with a sort name of the form columnname, or colname_subsort by
      * breaking it up, validating the bits that are presend, and returning them.
      * If there is no subsort, then $subsort is returned as ''.
      * @return array array($colname, $subsort).
@@ -1102,7 +1102,7 @@ class question_bank_view {
         $sorts = array();
         foreach ($this->sort as $sort => $order) {
             list($colname, $subsort) = $this->parse_subsort($sort);
-            $sorts[] = $this->knowncolumntypes[$colname]->sort_expression($order < 0, $subsort);
+            $sorts[] = $this->requiredcolumns[$colname]->sort_expression($order < 0, $subsort);
         }
 
     /// Build the where clause.