[lilypond-book] Fix `quote' + `line-width' option combination.

[lilypond-book] Fix `quote' + `line-width' option combination.

The previous code converted a snippet starting with

  \begin[quote]{lilypond}
  ...

into this LaTeX code

  \begin{quotation}
  {%
  \parindent 0pt
  ...

while

  \begin[quote, line-width=...]{lilypond}
  ...

was converted to

  \parindent 0pt
  ...

omitting the `quotation' environment.  This was neither documented nor
expected behaviour.