Fix crash in script_column when suggestAccidentals = ##t is used (issue163041)

[n . puttock]

Hi Reinhold,

This looks OK, but there's still a remaining problem which I've
mentioned in the bugtracker for #787.

The comment is too specific though, since it's nothing to do with
suggestAccidentals; it just happens that this regtest has two scripts
(i.e., an articulation + the accidental) stacked in one direction on two
of the notes.

Cheers,
Neil

http://codereview.appspot.com/163041