Fix crash when warning about first line of music.
Fix crash when warning about first line of music.

hillaryskye/abcjs,hbarudin/abcjs,hillaryskye/abcjs,gabrielsanchez/abcjs,gabrielsanchez/abcjs,hbarudin/abcjs,hbarudin/abcjs,gnavalesi/abcjs,gnavalesi/abcjs,gnavalesi/abcjs,gabrielsanchez/abcjs,hillaryskye/abcjs