Providing support to extend filters on the admin/user/user page

I need to provide another filter on the admin users list page. I altered user_filter_form and specified my required filter options and added submit handler which stores the required sessions. But when I submit the form, I am getting the following sql error.

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND' at line 1 query: SELECT COUNT(DISTINCT u.uid) FROM users u LEFT JOIN users_roles ur ON u.uid = ur.uid WHERE u.uid != 0 AND AND in /var/www/html/HZD-Enhancements/modules/user/user.admin.inc on line 145

I found that this query is depend on the filters returned by user_filters functions. To make it work I need to add my filter details to the array returned by user_filters function. It will be better to provide option to alter this array using drupal_alter function.

I added drupal_alter('admin_user_filters', $filters); statement in the user_filters function and wrote hook_admin_user_filters_alter function in my custom module to make it work.

I hope this is a required feature, so attaching a patch about the fix.