feat: add topicIndex to category page

public/src/client/category.js

@@ -41,10 +41,9 @@ define('forum/category', [
 	};
 
 	function handleScrollToTopicIndex() {
-		var parts = window.location.pathname.split('/');
-		var topicIndex = parts[parts.length - 1];
+		var topicIndex = ajaxify.data.topicIndex;
 		if (topicIndex && utils.isNumber(topicIndex)) {
-			topicIndex = Math.max(0, parseInt(topicIndex, 10) - 1);
+			topicIndex = Math.max(0, parseInt(topicIndex, 10));
 			if (topicIndex && window.location.search.indexOf('page=') === -1) {
 				navigator.scrollToElement($('[component="category/topic"][data-index="' + topicIndex + '"]'), true, 0);
 			}

src/controllers/category.js

@@ -96,6 +96,7 @@ categoryController.get = async function (req, res, next) {
 	categoryData.privileges = userPrivileges;
 	categoryData.showSelect = userPrivileges.editable;
 	categoryData.showTopicTools = userPrivileges.editable;
+	categoryData.topicIndex = topicIndex;
 	categoryData.rssFeedUrl = nconf.get('url') + '/category/' + categoryData.cid + '.rss';
 	if (parseInt(req.uid, 10)) {
 		categories.markAsRead([cid], req.uid);