[InterNetNews/inn] aaabec: Check an error cert is available before using

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: aaabec462ee5eb694b599a13bafcbc2f1db6bd22
      https://github.com/InterNetNews/inn/commit/aaabec462ee5eb694b599a13bafcbc2f1db6bd22
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2023-03-05 (Sun, 05 Mar 2023)

  Changed paths:
    M doc/pod/hacking.pod
    M nnrpd/tls.c

  Log Message:
  -----------
  Check an error cert is available before using

In verify_callback(), we need to check that an error cert is
available before printing its data.  Patch from upstream OpenSSL
(openssl/openssl at fad0f80eff188ef938fed614245a56ed56110deb, 2022-07-20).

Also, remove useless verify_error variable, and provide a link in
HACKING to the OpenSSL repository.