Correct mMidiOutputComplete, though it doesn't matter...

... Used to be, it became true too soon when play started after time 0, so
AudioIO::IsStreamActive() might become false too soon -- except that now there
is always a portaudio stream when there is a midi stream, so that didn't happen.

Mistake was to add mT0 to MidiTime(), which already has mT0 for its origin.

This error would affect nothing if you just let play to the end without trying
a keystroke command.  The error might have been enabling the wrong commands.

src/AudioIO.h

@@ -563,7 +563,7 @@ private:
    /// Track of next event
    NoteTrack        *mNextEventTrack;
    /// True when output reaches mT1
-   bool             mMidiOutputComplete;
+   bool             mMidiOutputComplete{ true };
    /// Is the next event a note-on?
    bool             mNextIsNoteOn;
    /// mMidiStreamActive tells when mMidiStream is open for output