FIX: Load subcategories through CategoryList (#26297)

When "lazy load categories" is enabled and parent_category_id was set,
the query fetching categories contained a contradiction filtering both
by parent_category_id and parent_category_id = NULL.

app/models/category_list.rb

@@ -140,7 +140,7 @@ class CategoryList
 
     query = self.class.order_categories(query)
 
-    if @guardian.can_lazy_load_categories?
+    if @guardian.can_lazy_load_categories? && @options[:parent_category_id].blank?
       page = [1, @options[:page].to_i].max
       query =
         query
@@ -154,7 +154,7 @@ class CategoryList
 
     @categories = query.to_a
 
-    if @guardian.can_lazy_load_categories?
+    if @guardian.can_lazy_load_categories? && @options[:parent_category_id].blank?
       categories_with_rownum =
         Category
           .secured(@guardian)

spec/models/category_list_spec.rb

@@ -437,5 +437,13 @@ RSpec.describe CategoryList do
         category.id,
       )
     end
+
+    context "with parent_category_id" do
+      it "returns subcategories" do
+        category_list = CategoryList.new(Guardian.new(user), parent_category_id: category.id)
+
+        expect(category_list.categories.size).to eq(1)
+      end
+    end
   end
 end