attempt to add with overflow error when parsing bytes

Reproduction test:

#[test]
fn too_long_bytes_length() {
    let data = vec![91, 255, 255, 255, 255, 255, 255, 255, 255];
    let mut de = minicbor::decode::Tokenizer::new(&data);

    assert!(matches!(
        de.token(),
        Err(minicbor::decode::Error::EndOfInput)
    ));
}

Will open PR tomorrow