Function make_sfx_backend 

pub fn make_sfx_backend(
    name: &str,
    client: Client,
    mm: &MMAudioOptions<'_>,
) -> Result<Option<Box<dyn SfxBackend>>>

make_sfx_backend(name, ...). Ok(None) means the caller should exit with status 1 (the error is already logged, as sys.exit(1) does).