MAGETWO-44444: Billing address is not set as shipping on one page checkout

added fallback to shipping address

Author: Serhiy Shkolyarenko

app/code/Magento/Checkout/view/frontend/web/js/model/shipping-save-processor/default.js

@@ -27,10 +27,11 @@ define(
         'use strict';
         return {
             saveShippingInformation: function() {
+                var billingAddress = quote.billingAddress() || quote.shippingAddress();
                 var payload = {
                     addressInformation: {
                         shipping_address: quote.shippingAddress(),
-                        billing_address: quote.billingAddress(),
+                        billing_address: billingAddress,
                         shipping_method_code: quote.shippingMethod().method_code,
                         shipping_carrier_code: quote.shippingMethod().carrier_code
                     }