Return the correct type for ASN.1 BOOLEANs

Return the correct type for ASN.1 BOOLEANs

ASN.1 BOOLEANs and ASN.1 NULL are handled specially in the ASN.1 sausage
factory and they are special in that they don't have a->value.ptr set.
Both need to be special cased here since they fail the a->type.ptr != NULL
check.

Apart from fixing an obvious bug in ASN1_TYPE_get(), this fixes another
crash in openssl(1) asn1parse. There is more to do in the vicinity, but
that is more complex and will have to wait for OpenBSD 7.3-current.

with/ok jsing