bug in 2.4.6 with add-grace-property and \midi block

[roland]

Using 2.4.6, if a \midi block is added to a .ly file containing a line
 #(add-grace-property ..., lilypond fails with the errors:
 
 GNU LilyPond 2.4.6
Processing `/cygdrive/D/LilyWork/Tests/add-grace-prop.ly'
Parsing...
Interpreting music... Backtrace:
In unknown file:
   ?:  0* [lilypond-main ("/cygdrive/D/LilyWork/Tests/add-grace-prop.ly")]
In /usr/share/lilypond/2.4.6/scm/lily.scm:
 337:  1* (let* ((failed #) (handler #)) (for-each (lambda # #) files) ...)
 339:  2* [for-each #<procedure #f #> #]
In /usr/share/guile/1.6/srfi/srfi-1.scm:
 663:  3  (if (null? rest) (letrec ((lp #)) (lp list1)) ...)
    ...
 667:  4  (begin (f (car l)) (lp (cdr l)))
 668:  5* [#<procedure #f (f)>
"/cygdrive/D/LilyWork/Tests/add-grace-prop.ly"]
In /usr/share/lilypond/2.4.6/scm/lily.scm:
 341:  6  [catch ly-file-failed #<procedure #f ()> #<procedure #f (key
arg)>]
In unknown file:
   ?:  7* [#<procedure #f ()>]
In /usr/share/lilypond/2.4.6/scm/lily.scm:
 341:  8* [ly:parse-file "/cygdrive/D/LilyWork/Tests/add-grace-prop.ly"]
In /usr/share/lilypond/2.4.6/ly/init.ly:
   7:  9* (if (pair? toplevel-scores) (ly:parser-print-book parser #))
   8: 10  [ly:parser-print-book #<my_lily_parser  > #<Book>]
In unknown file:
   ?: 11* [set-prop #<Context Voice=1 () >]
In /usr/share/lilypond/2.4.6/scm/music-functions.scm:
 548: 12* (let* (# # #) (ly:context-set-property! where # new-settings))
 549: 13* [ly:context-property () graceSettings]
/usr/share/lilypond/2.4.6/scm/music-functions.scm:549:21: In procedure
ly_context_property in expression (ly:context-property where (quote
graceSettings)):
/usr/share/lilypond/2.4.6/scm/music-functions.scm:549:21: Wrong type
argument in position 1 (expecting Translator group): ()





\version "2.4.6"
\include "english.ly"

\score {
        <<
        % you get the error if one (or both) of theese two lines is active
AND the midi block is active
                #(add-grace-property 'Voice 'Slur 'direction 1)
                #(add-grace-property 'Voice 'Stem 'direction -1)
                \relative c'' {a b c d e}
        \\
                \relative c'{a b c d e}
        >>

        \midi {
        }
                
        \layout {
        }
}