bug#45156: 28.0.50; Segfault due to glyph_row being set to NULL

[Eli Zaretskii]

> From: Torsten Bronger <bronger@physik.rwth-aachen.de>
> Date: Thu, 10 Dec 2020 08:55:59 +0100
> 
> I see Emacs segfaulting when moving the cursor upwards in a LaTeX
> document while tex-fold-mode is active.  The starting position of the
> cursor is important.
> 
> I placed all files to reproduce the bug at
> <http://wilson.bronger.org/emacs-glyph_row-bug.tar>.  The TeX file needs
> to be put in /tmp.  tex-fold-mode must be present.  Furthermore, place
> .emacs and .emacs.desktop in the proper positions, start current Git
> Emacs, and press the "cursor up" button.  Then, Emacs crashes for me.
> 
> The subject of this bug is just to give it a name.  I do not know
> whether glyph_row is the issue.  However, I bisected the problem, and it
> started with commit f425a774, which sets glyph_row to NULL in two
> places.  If I revert this commit, the problem is gone.

Ouch! what a terrible blunder!  Sorry about that; I see the problem
and am working on a solution.