Prevent sustain passing through when pressing shift+sustain

[thomasjwebb]

This might not be a big deal but I can imagine a situation where this annoys someone if the sustain passes through to a plugin when the person really just meant to switch pages. This could be done by setting the host midi out to only listen to a channel nothing is on (2) and manually pass all the non-sustain notes through manually. Easy fix but also feels like a lot of overhead so maybe only fix if someone complains about this.