UX: Disable dismiss notifications button when there is nothing to dismiss.

app/assets/javascripts/discourse/controllers/user-notifications.js.es6

@@ -14,6 +14,11 @@ export default Ember.ArrayController.extend({
     return length > 0;
   },
 
+  @computed('model.content.@each.read')
+  allNotificationsRead() {
+    return !this.get('model.content').some((notification) => !notification.get('read'));
+  },
+
   currentPath: Em.computed.alias('controllers.application.currentPath'),
 
   actions: {

app/assets/javascripts/discourse/templates/user/notifications.hbs

@@ -23,7 +23,8 @@
                class='btn dismiss-notifications'
                action="resetNew"
                label='user.dismiss_notifications'
-               icon='check'}}
+               icon='check'
+               disabled=allNotificationsRead}}
   {{/if}}
 </section>