Because MIDI triggers compute buffer-relative timestamps using
timeline_samples - start_sample, this already takes into account
any offset to the start of the trigger. We still need to use dest_offset
if a non-zero value was passed into ::midi_run(), but we do NOT
want to have it contain the "offset to start of trigger in process
cycle" as well. Instead of trying to special case
::maybe_compute_next_transition(), we just pass a dummy pframes_t
to that method, leaving dest_offset as it was passed into ::midi_run()
511b09b3d6