bug#20891: emacs: Back off if .doc is not an Office document

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Andreas Schwab <schwab@suse.de>,  rpluim@gmail.com,  era+emacs@iki.fi,
>   20891@debbugs.gnu.org,  stefan@marxist.se
> Date: Fri, 15 Nov 2019 08:51:40 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > But then AFAIK MS Word documents had different signatures for
> > different versions, so we should have several.
> 
> All .doc files allegedly start with the same eight bytes.

Maybe my reading of the 'magic' file is wrong, but it seems to say
otherwise.