* sm/certlist.c (gpgsm_add_to_certlist): Track expired error.  Make
the expired check easier to read by using if and case.

If all selected certificates are expired, don't mislead the user
saying that no certificate was found. Instead, return the error
of the first certificate selected.

* sm/certlist.c: if one expired certificate was found, don't return
  no certificate found, return instead the expiration error