MDL-54042 user: Fix debugging in core_user_get_users_by_field

The course object returned by enrol_get_all_users_courses does not include the defaultgroupingid.

This course object is passed to user_get_user_details - which does need
the defaultgroupingid.

All the other group info is returned (groupmode) etc - so it makes sense to also return this extra field.

lib/enrollib.php

@@ -789,6 +789,7 @@ function enrol_get_all_users_courses($userid, $onlyactive = false, $fields = NUL
     $basefields = array('id', 'category', 'sortorder',
             'shortname', 'fullname', 'idnumber',
             'startdate', 'visible',
+            'defaultgroupingid',
             'groupmode', 'groupmodeforce');
 
     if (empty($fields)) {