Check appropriate OSSL_PARAM_get_* functions for NULL

Check appropriate OSSL_PARAM_get_* functions for NULL

The base type OSSL_PARAM getters will NULL deref if they are initalized
as null.  Add NULL checks for those parameters that have no expectation
of returning null (int32/64/uint32/64/BN).  Other types can be left as
allowing NULL, as a NULL setting may be meaningful (string, utf8str,
octet string, etc).

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23083)