ExportMidi::writeHeader() only write default C sig if no initial key sig found
Need to fix bug described in https://musescore.org/en/node/184296 which I'm not going to reporduce here entirely, but the problem was that ExportMidi::writeHeader() would incorrectly write a default C keysig at tick 0 for every single time that when through any repeat list without finding a key signature.
Bug is in 2.0.3 and lastest 2.1-dev 3523f8f (but I haven't tested 3.0-dev).
I'll include export-as-midi_full-meas-intro.mscx:
as test file which when exported to midi should be like export-as-midi_full-meas-intro.mid, which when re-imported should looks like:
but which incorrectly looked like:
Which incorrectly appears to have no initial key sig, when it actually mistakenly had an initial Bb keysig followed immediately by an initial C key sig.