Percussion-related notes should always use fixed pitches in AddmusicM songs

[KungFuFurby]

This is an error that was accidentally discovered during an analysis of a song that had been constantly remoderated over the years, though the song's origins predate Addmusic405 and AddmusicM. It is a partial regression of #198 for AddmusicM songs only... but it applies to all channels.

It just so happens that a percussion note is constantly output while the instrument is set to @21-@30. This behavior applies to all channels in the AddmusicM adaptation, but not the Addmusic405 adaptation.

This also applies to Addmusic Java and carol's Addmusic.