Conform more code to strictNullChecks and noImplicitAny (#11156)

src/components/structures/ScrollPanel.tsx

@@ -830,6 +830,7 @@ export default class ScrollPanel extends React.Component<IProps> {
     }
 
     private topFromBottom(node: HTMLElement): number {
+        if (!this.itemlist.current) return -1;
         // current capped height - distance from top = distance from bottom of container to top of tracked element
         return this.itemlist.current.clientHeight - node.offsetTop;
     }