bug#63194: OpenMoji font is drawn invisibly

["Timo Wilken" <guix@twilken.net>]

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Some applications fail to draw the OpenMoji font packaged in Guix
(font-openmoji package). This includes LibreOffice Writer and Polybar
(both as packaged in Guix). Weirdly, gucharmap seems to draw the font
fine.

Any symbols in OpenMoji are drawn completely transparently, as far as
I can tell. They still take up as much space between other characters
as they should, but I can't see anything on a light or dark
background.

I've attached screenshots showing the problem (LibreOffice, polybar)
and of gucharmap drawing the font OK (with "View -> Show only symbols
from this font" enabled).

This started happening this week, when I upgraded Guix from 13ebf5e
(Guix home generation 284) to e86851c (Guix home generation 285). It
worked fine with Guix 13ebf5e and before.

--8<---------------cut here---------------start------------->8---
$ guix home list-generations
Generation 284	Apr 24 2023 20:06:13
  file name: /var/guix/profiles/per-user/timo/guix-home-284-link
  canonical file name: /gnu/store/lybmqggy29kc3v1z0ni5yslh79kbj0ga-home
  channels:
    [two non-free channels omitted]
    guix:
      repository URL: https://git.savannah.gnu.org/git/guix.git
      branch: master
      commit: 13ebf5e36cc676627a19072d3712c399b7aae61f
  configuration file: /gnu/store/x2l0c7mc4s279ygzrkkgf3hivzpr0n9b-configuration.scm
Generation 285	Apr 29 2023 20:09:47	(current)
  file name: /var/guix/profiles/per-user/timo/guix-home-285-link
  canonical file name: /gnu/store/18ls5dydwczwrgrshdfsdvmdyz6g88fa-home
  channels:
    [two non-free channels omitted]
    guix:
      repository URL: https://git.savannah.gnu.org/git/guix.git
      branch: master
      commit: 3676e312aaf1ce10ed1d7844e871b54e04624098
  configuration file: /gnu/store/sqpmz8y5lywkm2v8pc6cg5n3hy7kazrs-configuration.scm
--8<---------------cut here---------------end--------------->8---

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