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Doing a chdir("..") will not fail when the root directory is reached,
and when getcwd() keeps failing too, we have no way of knowing when
to stop.  So, simply limit the number of attempted chdirs, to avoid
getting into an endless loop.

This avoids the hang in https://savannah.gnu.org/bugs/index.php?47659

.
Reported-by: Chris Renshaw <osm0sis@outlook.com>
Signed-off-by: Benno Schulenberg <bensberg@justemail.net>