fix first reply insertion

public/src/client/topic/posts.js

@@ -123,9 +123,9 @@ define('forum/topic/posts', [
 
 		var after, before;
 
-		if (direction === 1) {
+		if (direction === 1 && repliesSelector.length) {
 			after = repliesSelector.last();
-		} else if (direction === -1) {
+		} else if (direction === -1 && repliesSelector.length) {
 			before = repliesSelector.first();
 		}
 

public/src/modules/navigator.js

@@ -197,7 +197,7 @@ define('navigator', ['forum/pagination', 'components'], function(pagination, com
 
 	navigator.scrollToPostIndex = function(postIndex, highlight, duration, offset) {
 		var scrollTo = components.get('post/anchor', postIndex);
-			
+
 		if (!scrollTo.length) {
 			navigator.scrollActive = false;
 			return;