fix #305069: Chord symbols attached to fret diagrams don't play back

[Jojo-Schmitz]

resolves https://musescore.org/en/node/305069

[MarcSabatella]

Nice! I figured it would be something like that, but hadn't checked to see where this happens.

I wonder if it's worth having a function "hasHarmonyPlayback" or something like that so we don't have to always check like this? It could also conceivably return false if the preference is off, or if the play property is off. And, it could conceivably return true for fret diagrams that don't have a chord symbol attached, if we ever implement direct playback of the voicing from the fret diagram itself.

But that kind of decision might want to wait until we definitively decide how we want ther default to work for chord symbol playback. To me this is still an open question we need to resolve, and I guess I ay just need to propose and implement something.

[Jojo-Schmitz]

Well, this method is used in 4 places, 2 of which just need to know whether or not there are harmonies and I'm not sure whether the other 2 really need the number.