gpg: Fix key expiration and usage for keys created at the Epoch.
* g10/getkey.c (merge_selfsigs_main): Take a zero key creation time in account.
Keys created at the Epoch have a creation time of 0; when figuring out
the latest signature with properties to apply to a key the usual
comparison A > B does not work if A is always 0. We now special case
this for the expiration and usage data.
(cherry picked from commit 161a098be6f9d50fb5f7e120baee81e75d6eb5ad)
- Co-authored-by: email@example.com
- GnuPG-bug-id: T4670
- Signed-off-by: Werner Koch <firstname.lastname@example.org>