sm: Fix use of value NONE in gnupg_isotime_t type.
* common/gettime.h (GNUPG_ISOTIME_NONE): New. * sm/call-dirmngr.c (gpgsm_dirmngr_isvalid): Use it. * sm/certlist.c (gpgsm_add_to_certlist): Likewise. * sm/import.c (check_and_store): Likewise. * sm/keylist.c (list_cert_colon, list_cert_raw): Likewise. (list_cert_std): Likewise. * sm/sign.c (gpgsm_sign): Likewise.
(cherry picked from commit 05fdaa1737523fad72b6ffb9e7a90d5344ff64a5)
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>