Fix inconsistent TPCs after repitch

[Reedbeta]

Resolves: #31567

The problem was that repitch left nval.tpc1 set to invalid, and then we'd set tpc1 directly from the MIDI pitch, leading to inconsistent values for tpc1 and tpc2. Instead, we should set tpc1 by transposing tpc2 if it's valid, and only use the MIDI pitch if both are invalid.

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[cbjeukendrup]

It seems that this also resolves #26681 / #31477