[trunk] SIGABORT when loading a score with parenthesized accidental(s)

Steps:
1) Open a score containing one or more parenthesized accidentals
2) Program aborts.

A sample score with just a single note with a parenthesized accidental is attached.

Call stack at abort:

file line function
accidental.cpp 149 Accidental::symbol
accidental.cpp 205 Accidental::layout()
layout.cpp 262 Score::layoutChords1()
layout.cpp 585 Score::layoutStage3()
layout.cpp 685 Score::doLayout()
score.cpp 622 Score::read()

Thanks,

M.