Add appropriate NULL checks in EVP_CIPHER api

Add appropriate NULL checks in EVP_CIPHER api

The EVP_CIPHER api currently assumes that calls made into several APIs
have already initalized the cipher in a given context via a call to
EVP_CipherInit[_ex[2]].  If that hasnt been done, instead of an error,
the result is typically a SIGSEGV.

Correct that by adding missing NULL checks in the apropriate apis prior
to using ctx->cipher

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22995)