Ensure buffer/length pairs are always in sync

Ensure buffer/length pairs are always in sync

Following on from CVE-2021-3449 which was caused by a non-zero length
associated with a NULL buffer, other buffer/length pairs are updated to
ensure that they too are always in sync.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>