#8618: Apply coupon code button issue on Checkout

- fixed issue with assigning coupon_code value from totals.

Author: mcspronko

Diff for: app/code/Magento/SalesRule/view/frontend/web/js/view/payment/discount.js

@@ -15,12 +15,14 @@ define([
 
     var totals = quote.getTotals(),
         couponCode = ko.observable(null),
-        isApplied = ko.observable(couponCode() != null);
+        isApplied;
 
     if (totals()) {
         couponCode(totals()['coupon_code']);
     }
 
+    isApplied = ko.observable(couponCode() != null);
+    
     return Component.extend({
         defaults: {
             template: 'Magento_SalesRule/payment/discount'