fix 404 when numbers at the end of url wp

add_action( 'template_redirect', 'so16179138_template_redirect', 0 );
function so16179138_template_redirect()
{
    if( is_singular() )
    {
        global $post, $page;
        $num_pages = substr_count( $post->post_content, '<!--nextpage-->' ) + 1;
        if( $page > $num_pages ){
            include( get_template_directory() . '/404.php' );
            exit;
        }
    }
}