[MusicXML] Instruments with less than five stave lines appear with five stave lines
1. Create Finger Snap score.
5. Open MusicXML.
Expected result: Stave has one line.
Actual result: Stave has five lines.
Discussion: Applies to other instruments that don't have five stave lines, such as 'Drumset 3 lines'.
Using MuseScore 2.0 Nightly Build (5597) - Mac 10.7.3.