FIX: Preload sidebar categories when lazy loading categories (#25332)

This fixes a bug where the sidebar categories would not be loaded when
the categories were lazy loaded because the sidebar uses the preloaded
category list, which was empty.

spec/serializers/site_serializer_spec.rb

@@ -131,12 +131,34 @@ RSpec.describe SiteSerializer do
     expect(serialized[:shared_drafts_category_id]).to eq(nil)
   end
 
-  it "does not include categories if lazy_load_categories" do
-    SiteSetting.lazy_load_categories_groups = "#{Group::AUTO_GROUPS[:everyone]}"
+  context "with lazy loaded categories enabled" do
+    fab!(:user)
+    let(:guardian) { Guardian.new(user) }
 
-    serialized = described_class.new(Site.new(guardian), scope: guardian, root: false).as_json
+    before { SiteSetting.lazy_load_categories_groups = "#{Group::AUTO_GROUPS[:everyone]}" }
 
-    expect(serialized[:categories]).to eq(nil)
+    it "categories does not include any categories for anonymous users" do
+      serialized = described_class.new(Site.new(guardian), scope: guardian, root: false).as_json
+
+      expect(serialized[:categories]).to eq(nil)
+    end
+
+    it "categories include only sidebar categories" do
+      Fabricate(:category_sidebar_section_link, linkable: category, user: user)
+
+      serialized = described_class.new(Site.new(guardian), scope: guardian, root: false).as_json
+
+      expect(serialized[:categories].map { |c| c[:id] }).to contain_exactly(category.id)
+    end
+
+    it "categories include only visible sidebar categories" do
+      Fabricate(:category_sidebar_section_link, linkable: category, user: user)
+      category.update!(read_restricted: true)
+
+      serialized = described_class.new(Site.new(guardian), scope: guardian, root: false).as_json
+
+      expect(serialized[:categories]).to eq(nil)
+    end
   end
 
   describe "#anonymous_default_navigation_menu_tags" do