[Trunk] Blank sound default in Mixer for scores that don't play that instrument
S4 - Minor
1. Open score including piano and vocals.
3. Go to Synthesiser.
4. Load soundfont with one instrument (piano).
(Result: Voice isn't heard)
5. Open Mixer.
(Result: Soundfont is listed as voice in sound, despite not being heard).
6. Click on the soundfont.
Result: Soundfont is now heard.
Discussion: I think by default (until selected), there should be a blank option that outputs no sound (see 1.0 behaviour for one such solution).
Using MuseScore 2.0 Nightly Build (4367) - Mac 10.6.7.
Fixed in branch master, commit 7a5c6d8640
Fix #11097: Ensure chord list is loaded for part scores too