cache_moderators() generates invalid query

This is a regression caused by one of the edits in PHPBB3-10484. The change to /includes/functions_admin.php uses the $sql_ary variable that is later expected to have been empty. Lines 2333 and 2360 should use a different variable name or it should be cleared out afterwards. Otherwise, the contents of the first query gets pulled into the generation of the next one, which is incorrect.