In proc_parser_roa() adjust the expiry calculation to walk all of

In proc_parser_roa() adjust the expiry calculation to walk all of
the auth tree (including the TA) and be more careful to not dereference
NULL pointers. Both valid_ski_aki() and get_crl() can return NULL
pointers. In these situations X509_verify_cert() should fail and
the affected code should be not reachable but better be prepared.
With and OK tb@