Fix #12760: Case sensitivity of filter on manage user page

The Manage User page provides a filter for the first letter of
usernames. This filter doesn't work if the database is case sensitive.

Signed-off-by: David Hicks <hickseydr@optusnet.com.au>

manage_user_page.php

@@ -153,7 +153,7 @@
 		$t_where = db_helper_compare_days("" . db_now() . "","date_created","<= $days_old");
 	} else {
 		$c_prefix = db_prepare_string($f_filter);
-		$t_where = "(username like '$c_prefix%')";
+		$t_where = "(UPPER(username) LIKE '$c_prefix%')";
 	}
 
 	$p_per_page = 50;