#4963 bracketify-stencil and similar fail with \key c \major stencil

[Simon Albrecht]

Reported by Rutger Hofman.

\version "2.19.47"

{
  % http://lsr.di.unimi.it/LSR/Snippet?id=647
  \override Staff.KeySignature.stencil = #(lambda (grob) (bracketify-stencil (ly:key-signature-interface::print grob) Y 0.1 0.2 0.1))
  \key c \major
  c''
}

=>

Parsing...
Interpreting music...
Preprocessing graphical objects...lilypond: /home/gub/NewGub/gub/target/linux-64/src/lilypond-git.sv.gnu.org--lilypond.git-release-unstable/lily/skyline.cc:94: Building::Building(Real, Real, Real, Real): Assertion `start_height == end_height' failed.

With parenthesize-stencil, the log reads:

Parsing...
Interpreting music...
Preprocessing graphical objects...
programming error: Improbable offset for stencil: -nan staff space
Setting to zero.
continuing, cross fingers
programming error: Infinity or NaN encountered
continuing, cross fingers
/tmp/frescobaldi-07y0Mg/tmpPOmx3w/document.ly:6:3: programming error: Infinity or NaN encountered

  \key c \major
/tmp/frescobaldi-07y0Mg/tmpPOmx3w/document.ly:6:3: continuing, cross fingers
programming error: Infinity or NaN encountered
continuing, cross fingers
programming error: Improbable offset for stencil: -nan staff space
Setting to zero.
continuing, cross fingers
programming error: Improbable offset for stencil: -nan staff space
Setting to zero.
continuing, cross fingers
programming error: Infinity or NaN encountered
continuing, cross fingers
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

The procedures are defined in scm/stencil.scm.