remux example fails on sample MKV file

[astraw]

Steps to reproduce:

1. Download sample_640x360.mkv from https://filesamples.com/formats/mkv (probably many mkv files would work, I just was looking for a sample and found this).
2. Run the remuxer on this file:

RUST_LOG=debug cargo run --example matroska_remux -- -i sample_640x360.mkv -o remux.mkv

(As a side note, if RUST_LOG is not set, the program exits with exit code 0 but the created file is incomplete.)

3. Observe the error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: InvalidData', examples/matroska_remux.rs:55:62
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[Luni-4]

@FreezyLemon

Does this sample work with your last changes?

[FreezyLemon]

No, it doesn't work either.