fix: userOnline can render as null, causing the page to break

Author: imorland

framework/core/js/src/forum/components/PostUser.js

@@ -68,7 +68,10 @@ export default class PostUser extends Component {
 
     items.add('avatar', avatar(user, { className: 'PostUser-avatar' }), 100);
 
-    items.add('userOnline', userOnline(user), 90);
+    const onlineIndicator = userOnline(user);
+    if (onlineIndicator) {
+      items.add('userOnline', onlineIndicator, 90);
+    }
 
     items.add('username', username(user), 80);