Ensure our buffer allocation allows for the Explicit IV

Ensure our buffer allocation allows for the Explicit IV

Some ciphers/protocol versions have an explicit IV. We need to make sure we
have sufficient room for it in the underlying buffer.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20087)