8b09becf1d
our policy is that "mute works on outputs", which means that mute should have no effect on what an instrument plugin does. However, MidiTrack::act_on_mute() used to inject sustain=0 messages into the data flow, which would affect the instrument plugin(s) in the track. now, MidiTrack::act_on_mute() simply notifies all Delivery objects in the track that a MIDI mute is needed via a channel mask. The Delivery objects notice this during their ::run() method, and deliver the required MIDI events to their output ports. There is still a potential issue that Amp objects which notice they have been muted also send a similar set of messages. This needs more investigation and possibly other changes. But this commit allows a sustained note to return after the track is muted midway through it.
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