Core dump in version 2.25.7 (regression)

   Hi,

   The following non-minimum example results in a core dump, when I
   process it using 2.25.7 in Linux, it doesn't crash with 2.24.2. I've
   attempted to cut it down to a smaller example, but as soon as I comment
   out some lines from partI, it doesn't crash.

   As you can guess, the equivalence of the empty \partII in my actual
   score, is just included as a template to be filled in later, but I
   certainly want to be able to process it in this state without crashing.
   Removing \partII from the score gives the desired output.

   \version "2.25.7"
   partI = \relative c' {
   \repeat volta 2 {
   c8. 16 e8. 16 g8. 16 c8. 16 |
   \afterGrace g'1-\trill ( {f16 g ) } |
   a8. f16 a8. f16 a8. f16 d8. a16 |
   b8. d16 g8. fis16 \acciaccatura fis8 g2 |
   g,,8. 16 b8. 16 d8. 16 g8. 16 |
   \afterGrace d'1-\trill ( {c16 d ) } |
   e4.-! a,8 4.-\trill ( g16 a ) |
   fis'4.-! b,8 4.-\trill ( a16 b ) |
   g'4.-! e8 gis4.-\trill ( fis16 gis ) |
   a4 a,8. b16 c8. d16 \grace d8 e4 |
   d-! r c-! r |
   bes r r2 |
   a8. g16 a8. b16 c8. b16 c8. d16 |
   b8. a16 b8. c16 d8. c16 d8. e16 |
   c16-! ( d e8 ) c16-! ( d e8 ) c16-! ( d e8 ) c16-! ( d e8 ) |
   \grace g,8 fis4 e8 d g16 ( fis8. ) e16 ( d8. ) |
   d'4-! c-! r8 b c8. a16 |
   b8. g'16 fis8. g16 fis8. g16 fis8. g16 |
   a,16 ( b c8 ) b8. g16 \grace b8 a2-\trill |
   \alternative{
   \volta 1 { g1 | }
   \volta 2 {
   \time 12/8
   \tempo "Allegro"
   g4 r8 r4 r8 r2. |}}}
   \repeat volta 2 {
   }
   }
   partII = \fixed c' {
   \repeat volta 2 {
   \alternative{
   \volta 1 { }
   \volta 2 {
   \time 12/8
   \tempo "Allegro"
   }}}
   \repeat volta 2 {
   }}
   \score{
     \new StaffGroup <<
       \new Staff \partI
       \new Staff \partII
     >>
   }

      /Mats