dssenh: Only fill hash buffer when it's provided.

dlls/dssenh/main.c

@@ -940,7 +940,7 @@ BOOL WINAPI CPGetHashParam( HCRYPTPROV hprov, HCRYPTHASH hhash, DWORD param, BYT
             SetLastError( ERROR_MORE_DATA );
             return FALSE;
         }
-        memcpy( data, hash->value, hash->len );
+        if (data) memcpy( data, hash->value, hash->len );
         *len = hash->len;
         return TRUE;
 

dlls/dssenh/tests/dssenh.c

@@ -472,9 +472,16 @@ static void test_hash(const struct hash_test *tests, int testLen)
         ok(result && (hashLen == tests[i].hashLen), "Expected %d hash len, got %d.Error: %x\n",
             tests[i].hashLen, hashLen, GetLastError());
 
+        dataLen = 0xdeadbeef;
+        result = CryptGetHashParam(hHash, HP_HASHVAL, 0, &dataLen, 0);
+        ok(result, "Expected hash value return.\n");
+        ok(dataLen == hashLen, "Expected hash length to match.\n");
+
+        hashLen = 0xdeadbeef;
         result = CryptGetHashParam(hHash, HP_HASHVAL, hashValue, &hashLen, 0);
         ok(result, "Expected hash value return.\n");
 
+        ok(dataLen == hashLen, "Expected hash length to match.\n");
         ok(!memcmp(hashValue, tests[i].hash, tests[i].hashLen), "Incorrect hash output.\n");
 
         result = CryptHashData(hHash, data, dataLen, 0);