#5234 Segfault when music is empty and only MIDI file is generated

[Simon Albrecht]

The following code generates a segfault using 2.19.80 (Ubuntu 16.04, 64-bit):

\version "2.19.80"
\score {
  \new StaffGroup {}
  \midi {}
}

$ lilypond debug.ly
GNU LilyPond 2.19.80
Processing `debug.ly'
Parsing...
Interpreting music...
warning: no music found in score
MIDI output to `debug.midi'...Segmentation fault (core dumped) 

[Federico Bruni]

It's not only with StaffGroup, but also with Staff or Voice.
If \layout is present, the 'no music' warning is printed but the complation completes without crashing.
If only \midi is enabled, there's a crash.

\version "2.19.84"

\score {
  \new Staff {}
  %\new Voice { }
  %\layout {}
  \midi {}
}

[Federico Bruni]

Issue [#5246] is related