bug#58363: [PATCH 3/3] Improve error data signaled by sqlite-execute et al.

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Date: Fri, 21 Oct 2022 23:06:36 +0200
> 
> +  Lisp_Object ext_errcode = make_fixnum (sqlite3_extended_errcode (sdb));
> +  const char *errmsg = sqlite3_errmsg (sdb);
> +  return list4 (errstr, errmsg ? build_string (errmsg) : Qnil,
> +             errcode, ext_errcode);                      ^^^^

Is that Qnil really a good idea here?  What will an error message look
like in that case?  We may wish replacing Qnil with some standard
text, if it looks better.