FIX: ensures category order keeps consistent (#10165)

Before this change:
- first full page load would get category defaults defined un cateory settings
- a navigation to a topic and then back to categories list would reset defaut to the ones defined in discovery/topics

app/assets/javascripts/discourse/app/controllers/discovery/topics.js

@@ -21,7 +21,7 @@ const controllerOpts = {
   showTopicPostBadges: not("discoveryTopics.new"),
   redirectedReason: alias("currentUser.redirected_to_top.reason"),
 
-  order: "default",
+  order: null,
   ascending: false,
   expandGloballyPinned: false,
   expandAllPinned: false,
@@ -37,11 +37,11 @@ const controllerOpts = {
     changeSort(sortBy) {
       if (sortBy === this.order) {
         this.toggleProperty("ascending");
+        this.model.refreshSort(sortBy, this.ascending);
       } else {
         this.setProperties({ order: sortBy, ascending: false });
+        this.model.refreshSort(sortBy, false);
       }
-
-      this.model.refreshSort(sortBy, this.ascending);
     },
 
     // Show newly inserted topics

lib/topic_query.rb

@@ -684,6 +684,9 @@ class TopicQuery
         if sort_order
           options[:order] = sort_order
           options[:ascending] = !!sort_ascending ? 'true' : 'false'
+        else
+          options[:order] = 'default'
+          options[:ascending] = 'false'
         end
       end
     end