fix: unread count in post stream not visible (#3791)

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

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

@@ -41,6 +41,7 @@ export default class PostStreamScrubber extends Component {
       const newStyle = {
         top: 100 - unreadPercent * 100 + '%',
         height: unreadPercent * 100 + '%',
+        opacity: unreadPercent ? 1 : 0,
       };
 
       if (vnode.state.oldStyle) {