Do not allow page breaks on the first column of a score (issue 581720054 by address@hidden)

[thomasmorley65]

I've applied your patch and did some testings.

It indeed solves the code given with boom.ly at
https://sourceforge.net/p/testlilyissues/issues/5801/

Though, I posted two minimals there.
While the first one now compiles fine, the second still crashes with:

GNU LilyPond 2.21.0
Processing `atest-99.ly'
Parsing...
Interpreting music...[8][16][24][24]
Preprocessing graphical objects...
Calculating page and line breaks (1 possible page breaks)...[1]
Drawing systems...
Layout output to `/tmp/lilypond-n0vRDz'...
Converting to `atest-99.pdf'...
Deleting `/tmp/lilypond-n0vRDz'...
Interpreting music...
Preprocessing graphical objects...lilypond:
/home/hermann/lilypond-git-guile-2.2/lily/constrained-breaking.cc:481:
void Constrained_breaking::initialize(Paper_score*, const
std::vector<long unsigned int>&): Assertion `pagebreak_col_indices[i] >
pagebreak_col_indices[i - 1]' failed.
Aborted (core dumped)

Probably
https://sourceforge.net/p/testlilyissues/issues/5767/
is related as well.

https://codereview.appspot.com/581720054/