bug#2631: get-free-disk-space when default-directory doesn't exist

[Kevin Ryde]

Eli Zaretskii <eliz@gnu.org> writes:
>
> Doesn't chdir need certain rights?

Only search perms in the parent directories leading to a given dir, I
believe.

I suppose the root dir could be unreadable/unsearchable too.  Dunno what
chdir would do in that case (I'm not brave enough to try it either!) but
certainly if the root dir is unsearchable then no subdir can work.