bug#19822: url-retrieve: allow to fail when no document is associated with the URI

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Tue, 1 Oct 2019 17:13:34 +0200
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, 19822@debbugs.gnu.org, Ivan Shmakov 
> <ivan@siamics.net>
> 
> However, I did provide a patch to obsolete the Netscape code, as a
> special case.  Please let me know if that patch should be installed or
> not -- either way is fine with me.

I'll let Lars decide.

Thanks.