fix problem when notification subscription isn't found

src/App.vue

@@ -362,6 +362,20 @@ export default class App extends Vue {
         );
       });
 
+    if (!subscription) {
+      // there is no endpoint or auth for the server to compare, so we're done
+      this.$notify(
+        {
+          group: "alert",
+          type: "info",
+          title: "Finished",
+          text: "Notifications are off.", // a different message so I know there are none stored
+        },
+        5000,
+      );
+      return true;
+    }
+
     const serverSubscription = {
       ...subscription,
     };