Fix bug in EVP_CIPHER_CTX_get_iv_length()

Out of range values could possibly be returned due to a lack of range checking.
Very unlikely to be exploitable for our provider because sensible values are
returned for all ciphers.

Also fixed the defaulting code so that the cipher's IV length is returned if
the cipher ctx doesn't support getting.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/18875)