Vibrato (wavy lines) notation

[Richard Shann]

I have been using a bit of code written by Mark Witmer to achieve wavy
lines above a series of notes. It co-opts the trill spanner mechanism
for this. 
I just found a bug in that code. When there is a line break the
calculation of
 (ly:grob-property grob  'X-extent)
      - with the grob being a #<Grob TrillSpanner > - 
then the value (+inf.0 -inf.0) is returned and in consequence an error
is thrown later when the value is used.
Unfortunately, I don't know what the status of the original file is or
where it came from, but attached is a version which prevents the error
being thrown by returning 0 instead. This results in the wavy line
running off the right margin but the typesetting at least succeeds.
I'm sending this in case anyone else has this problem or needs to
typeset vibrato marks, and - just in case - someone can suggest a
correct way to handle line breaks with these vibrato markings.

Richard Shann

vibrato.ily
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