catch exception from loading landingPageContent

embed-html.js : promise() : include .catch() in the result value; this was to address an issue seen May31, possibly with rootURL: /app/; possibly not tested to confirm this change works and is necessary.

frontend/app/components/elem/embed-html.js

@@ -128,6 +128,7 @@ export default Component.extend({
         imgs.attr('src', function (index, val) { return val.replace(/^/, path + '/'); });
       });
     });
+    promise = 
     promise.catch(
       function (/*jqXHR, statusText,*/ error) {
         let callbackContext = this,