Fix renderHeight being undefined (microsoft#165373)

Author: lramos15

src/vs/workbench/contrib/timeline/browser/timelinePane.ts

@@ -328,7 +328,7 @@ export class TimelinePane extends ViewPane {
 		let pageSize = this.configurationService.getValue<number | null | undefined>('timeline.pageSize');
 		if (pageSize === undefined || pageSize === null) {
 			// If we are paging when scrolling, then add an extra item to the end to make sure the "Load more" item is out of view
-			pageSize = Math.max(20, Math.floor((this.tree.renderHeight / ItemHeight) + (this.pageOnScroll ? 1 : -1)));
+			pageSize = Math.max(20, Math.floor((this.tree?.renderHeight ?? 0 / ItemHeight) + (this.pageOnScroll ? 1 : -1)));
 		}
 		return pageSize;
 	}