Ensure that NULL r and s parameters cannot be set on DSA_SIG/ECDSA_SIGs.

Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NEmilia Käsper <emilia@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1193)

crypto/dsa/dsa_asn1.c

@@ -34,6 +34,8 @@ void DSA_SIG_get0(BIGNUM **pr, BIGNUM **ps, const DSA_SIG *sig)
 
 int DSA_SIG_set0(DSA_SIG *sig, BIGNUM *r, BIGNUM *s)
 {
+    if (r == NULL || s == NULL)
+        return 0;
     BN_clear_free(sig->r);
     BN_clear_free(sig->s);
     sig->r = r;

crypto/ec/ec_asn1.c

@@ -1182,6 +1182,8 @@ void ECDSA_SIG_get0(BIGNUM **pr, BIGNUM **ps, const ECDSA_SIG *sig)
 
 int ECDSA_SIG_set0(ECDSA_SIG *sig, BIGNUM *r, BIGNUM *s)
 {
+    if (r == NULL || s == NULL)
+        return 0;
     BN_clear_free(sig->r);
     BN_clear_free(sig->s);
     sig->r = r;