fix #311353: Playback fix for half-diminished chords

[Mystic-Slice]

Resolves: https://musescore.org/en/node/311353

The 7th note is automatically added to the half-diminished chord without the need for specifying it.

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[MarcSabatella]

I can see that this would fix the issue with respect to playback. I also see that in chordlist.cpp, we already set the quality to half-diminished and set an "HChord" (a data structure that isn't used as much as it probably could be) to include the seventh. So I think everything is covered here.

[Jojo-Schmitz]

rebase needed

[Mystic-Slice]

@Jojo-Schmitz Done.

[Jojo-Schmitz]

thanks

[Jojo-Schmitz]

Any reason not to merge this one?