prune: close directory earlier during loose-object directory traversal

prune: close directory earlier during loose-object directory traversal

27e1e22d (prune: factor out loose-object directory traversal, 2014-10-16)
introduced a new function for_each_loose_file_in_objdir() with a helper
for_each_file_in_obj_subdir(). The latter calls callbacks for each file
found during a directory traversal and finally also a callback for the
directory itself.

git-prune uses the function to clean up the object directory. In
particular, in the directory callback it calls rmdir(). On Windows XP,
this rmdir call fails, because the directory is still open while the
callback is called. Close the directory before calling the callback.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>