Related fdo#60338: Create missing temp file dir with user's original umask

For one, that is consistent with how ensuredir (in the same .cxx) has always
worked, and for another saves us from trouble with umask, cf.
034d4c111976f337877e5954c6cc95ed9f90a343 "Related fdo#60338: Setting umask for
osl::Directory::open is useless."

Change-Id: Ic3fb5bb29ca3031d257067a514cb9f5bccfbfe4f