Check for V_ASN1_BOOLEAN/V_ASN1_NULL in X509_ATTRIBUTE_get0_data

The member value.ptr is undefined for those ASN1 types.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9278)

(cherry picked from commit 94f4d58a87eac9c6fe4cb46b998656bd6d6f03a5)