g10: Fix iteration over getkey results.
* g10/getkey.c (getkey_next): Fix invocation of 'lookup'. If we want to use RET_FOUND_KEY, RET_KEYBLOCK must be valid.
- Fixes-commit: 8ea72a776a88f3c851e812d258355be80caa1bc1
- Signed-off-by: Justus Winter <justus@g10code.com>