MDL-32791 quiz db: clean up garbage data that was causing problems.

Melinda Kraft reported having rows in their quiz_question_instances
table which caused various problems. These rows are meaningless, so I
have done a DB upgrade step to clean them up, which should deal with the
bad side-effets they were causing.

mod/quiz/db/upgrade.php

@@ -1196,6 +1196,17 @@ function xmldb_quiz_upgrade($oldversion) {
     // Moodle v2.2.0 release upgrade line
     // Put any upgrade step following this
 
+    if ($oldversion < 2011112903) {
+
+        // MDL-32791 somebody reported having nonsense rows in their
+        // quiz_question_instances which caused various problems. These rows
+        // are meaningless, hence this upgrade step to clean them up.
+        $DB->delete_records('quiz_question_instances', array('question' => 0));
+
+        // Quiz savepoint reached.
+        upgrade_mod_savepoint(true, 2012061702, 'quiz');
+    }
+
     return true;
 }
 

mod/quiz/version.php

@@ -25,7 +25,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$module->version   = 2011112902;       // The current module version (Date: YYYYMMDDXX)
+$module->version   = 2011112903;       // The current module version (Date: YYYYMMDDXX)
 $module->requires  = 2011112900;       // Requires this Moodle version
 $module->component = 'mod_quiz';       // Full name of the plugin (used for diagnostics)
 $module->cron      = 60;