DER writer: Add the possibility to abandon empty SEQUENCEs
In some cases, a SEQUENCE that contains only optional fields may end
up empty. In some cases, this may be represented by dropping the
SEQUENCE entirely from the encoded DER.
To do this, we detect the case where WPACKET_FLAGS_ABANDON_ON_ZERO_LENGTH
is used, and adapt accordingly.
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11710)