bug#28299: don't throw away what the user entered when he should enter a non-directory file name

[Katsumi Yamaoka]

On Thu, 31 Aug 2017 04:14:15 +0800, Dan Jacobson wrote:
> o runs the command gnus-mime-save-part.

> If one enters just /tmp
> then one sees
> "Please enter a non-directory file name"
> which is fine, except it *throws away /tmp*,
> and we have to enter /tmp/a instead of just continuing with /a .

Well, I think it's not necessarily a bug, but that feature looks
useful.  I've made a change in the Emacs git master as follows:

<http://lists.gnu.org/archive/html/emacs-diffs/2017-08/msg00348.html>

Thanks.