[IAP]Throw an error when the order.productId is undefined

If the order.produectId is undefined, when passing it to
navigator.iap.purchase() method, the Promise should be rejected and
an error named "InvalidAccessError" is thrown also.

BUG=XWALK-6895

iap/iap.js

@@ -64,6 +64,9 @@ exports.purchase = function(order) {
     if (!g_initialized) {
       throw new DOMError("InvalidStateError");
     }
+    if (typeof(order.productId) === "undefined") {
+      throw new DOMError("InvalidAccessError");
+    }
     var requestId = createAsyncRequest(resolve, reject);
     sendAsycRequest("purchase", requestId, order);
   });