Fix MIDI note off with velocity = 0
Thanks for this awesome MIDI UART example app!
According to this source, the note off command is also expressed via setting the velocity to 0: https://ibex.tech/resources/geek-area/communications/midi/midi-comms
Without this patch, the notes keep playing on my Novation Launchkey Mini MK3 (and going down the scale is quirky). With this patch applied, everything works so far :)