fix(status_list): Guard against missing ref (#4353)

app/javascript/mastodon/components/status_list.js

@@ -31,16 +31,18 @@ export default class StatusList extends ImmutablePureComponent {
   intersectionObserverWrapper = new IntersectionObserverWrapper();
 
   handleScroll = debounce(() => {
-    const { scrollTop, scrollHeight, clientHeight } = this.node;
-    const offset = scrollHeight - scrollTop - clientHeight;
-    this._oldScrollPosition = scrollHeight - scrollTop;
-
-    if (250 > offset && this.props.onScrollToBottom && !this.props.isLoading) {
-      this.props.onScrollToBottom();
-    } else if (scrollTop < 100 && this.props.onScrollToTop) {
-      this.props.onScrollToTop();
-    } else if (this.props.onScroll) {
-      this.props.onScroll();
+    if (this.node) {
+      const { scrollTop, scrollHeight, clientHeight } = this.node;
+      const offset = scrollHeight - scrollTop - clientHeight;
+      this._oldScrollPosition = scrollHeight - scrollTop;
+
+      if (250 > offset && this.props.onScrollToBottom && !this.props.isLoading) {
+        this.props.onScrollToBottom();
+      } else if (scrollTop < 100 && this.props.onScrollToTop) {
+        this.props.onScrollToTop();
+      } else if (this.props.onScroll) {
+        this.props.onScroll();
+      }
     }
   }, 200, {
     trailing: true,