Fix "Cannot read property" on missing status (#3322)

I've found this issue when I clicked replies to muted user on the timeline.

Properties I've removed in here were added with lazy loading using
IntersectionObserver (8e4d1cba), but those statuses are not need to be
tracked anyway because it will be rendered as only empty div.

app/javascript/mastodon/components/status.js

@@ -111,7 +111,7 @@ class Status extends ImmutablePureComponent {
     const { isHidden } = this.state;
 
     if (status === null) {
-      return <div ref={this
.n>handleRef} data-id={status.get('id')} />;
+      return null;
     }
 
     if (isIntersecting === false && isHidden) {