fix: #11440, update timestamp on lastpost button

public/src/client/topic/posts.js

@@ -36,7 +36,7 @@ define('forum/topic/posts', [
 		Posts.modifyPostsByPrivileges(data.posts);
 
 		updatePostCounts(data.posts);
-
+		updateNavigatorLastPostTimestamp(data.posts[0]);
 		updatePostIndices(data.posts);
 
 		ajaxify.data.postcount += 1;
@@ -53,6 +53,10 @@ define('forum/topic/posts', [
 		});
 	};
 
+	function updateNavigatorLastPostTimestamp(post) {
+		$('.pagination-block .pagebottom .timeago').timeago('update', post.timestampISO);
+	}
+
 	Posts.modifyPostsByPrivileges = function (posts) {
 		posts.forEach(function (post) {
 			post.selfPost = !!app.user.uid && parseInt(post.uid, 10) === parseInt(app.user.uid, 10);