[manolo]

Resolves: #35454

Backport of musescore/muse_framework#401 to 4.7. VstAudioClient::ensureActivity() no longer activates the component until setupProcessing() has succeeded. Exporting all parts of the score from the issue 8 times on this branch: 1 complete export out of 8 without the change, 8 out of 8 with it.

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