function sw_custom_post_type_includes($query) {
    if(isset($_GET['post_type']) && is_search() && is_main_query() && $query->query_vars['post_type'] != 'nav_menu_item'){
        $query->set('post_type', urldecode($_GET['post_type']));
    }
}
add_filter('pre_get_posts', 'sw_custom_post_type_includes');