bug#58028: 29.0.50; Ensures no leakage of glyph_matrix

[Eli Zaretskii]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: 58028@debbugs.gnu.org
> Date: Sat, 24 Sep 2022 17:31:20 +0200
> 
> So I've tested emacs -Q a bit (compiled with --enable-checking=all) with
> the attached patch.  I had no error so far.

Thanks, installed.

Please in the future mention the bug number in the commit log message
(I added it for you this time).