Ensure correct message length after parsing

[fabien-gigante]

After parsing the message length was not properly set in multiple cases. Which doesn't allow for instance to use those messages as is with send(). Typical usage below.

  LocalMIDI.setHandleMessage([](const midi::Message<128>& msg) { RemoteMIDI.send(msg); });
  RemoteMIDI.setHandleMessage([](const midi::Message<128>& msg) { LocalMIDI.send(msg); });