fix: selector for nav scroll

harmony doesn't have topic-header, they all have topic-main-buttons

public/src/modules/navigator.js

@@ -662,7 +662,7 @@ define('navigator', [
 
 		const postHeight = scrollTo.outerHeight(true);
 		const navbarHeight = components.get('navbar').outerHeight(true) || 0;
-		const topicHeaderHeight = $('.topic-header').outerHeight(true) || 0;
+		const topicHeaderHeight = $('.topic-main-buttons').outerHeight(true) || 0;
 		const viewportHeight = $(window).height();
 
 		// Temporarily disable navigator update on scroll