Fix build with Rust 1.53; we can't use map_while

        .map_err(dir_read_failed) // Result from fs::read_dir

        .into_iter()

        .flatten()

        .map_while(|result| result.map_err(dir_read_failed).ok()); // Result from dir.next()

        // TODO: Use map_while once we are on Rust >= 1.57

        .map(|result| result.map_err(dir_read_failed).ok()) // Result from dir.next()

        .take_while(|result| result.is_some())

        .flatten();

    for entry in entries {

        let path = entry.path();