fix error when single columns mode. (#4734)

app/javascript/mastodon/features/ui/components/columns_area.js

@@ -57,8 +57,10 @@ export default class ColumnsArea extends ImmutablePureComponent {
   }
 
   handleChildrenContentChange() {
+    if (!this.props.singleColumn) {
       scrollRight(this.node);
     }
+  }
 
   handleSwipe = (index) => {
     this.pendingIndex = index;