keep note-offs in demo_wav2midi.py

[jjburred]

thanks for the great library!

I noticed many note off events were filtered by demo_wav2midi.py, resulting in a lot of sustained notes in the MIDI output, so I modified the note filtering condition to include all note off triplets starting with 0.

Also, I added some checks to avoid trying to call mido with note or velocity values higher than 127, which results in an error.

[jjburred]

I see a macos compilation check failed on the aubio.aubio pipeline, but can't figure out why since I only modified a Python utility script