agent: Fix wiping memory in PKDECRYPT command.
* agent/pkdecrypt.c (ecc_kem_decrypt): Don't touch the memory when KEK is NULL.
- Fixes-commit: 57a3d2392539167767578dbb1414ad1cfb2a84ab
- GnuPG-bug-id: GnuPG-bug-id: T7893
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>