Ensure ECDSA_size always returns >= 0

Fixes #10484

Signed-off-by: William Brawner <me@wbrawner.com>

crypto/ec/ec_asn1.c

@@ -1297,5 +1297,7 @@ int ECDSA_size(const EC_KEY *r)
     i = i2d_ASN1_INTEGER(&bs, NULL);
     i += i;                     /* r and s */
     ret = ASN1_object_size(1, i, V_ASN1_SEQUENCE);
+    if (ret < 0)
+        return 0;
     return ret;
 }