Fix 1770: revert caused a crash in displayLilyMusic. (issue4805043)

[n . puttock]

Hi Reinhold,

LGTM, though I wonder whether it'd be better just to junk 'grob-property
and use 'grob-property-path exclusively.

Cheers,
Neil


http://codereview.appspot.com/4805043/diff/1/input/regression/display-lily-tests.ly
File input/regression/display-lily-tests.ly (right):

http://codereview.appspot.com/4805043/diff/1/input/regression/display-lily-tests.ly#newcode222
input/regression/display-lily-tests.ly:222: \test "NOT A BUG" ##[
\oneVoice #]    % resetting a bunch of properties
can you add some tests for nested properties too?

http://codereview.appspot.com/4805043/diff/1/scm/define-music-display-methods.scm
File scm/define-music-display-methods.scm (right):

http://codereview.appspot.com/4805043/diff/1/scm/define-music-display-methods.scm#newcode884
scm/define-music-display-methods.scm:884: (properties      (if (pair?
property-path)
(properties (ly:music-property expr 'grob-property-path
                               (list (ly:music-property expr
'grob-property))))

(same for OverrideProperty)

http://codereview.appspot.com/4805043/diff/1/scm/define-music-display-methods.scm#newcode892
scm/define-music-display-methods.scm:892: (if (and (pair? properties)
(null? (cdr properties)))
remove pair? check

http://codereview.appspot.com/4805043/