Fix for #2488 - parse contents of search results of type=Category (#2496)

* Fix for #2488 - parse contents of search results of type=Category (returned on first page for universal (type=all) queries instead of returning an error.

* Moved content array walker to Category#to_json

As requested by reviewer this change moves the content array walker from the API endpoint to the Category class.

* Update src/invidious/helpers/serialized_yt_data.cr

Co-authored-by: syeopite <70992037+syeopite@users.noreply.github.com>

src/invidious/helpers/serialized_yt_data.cr

@@ -237,8 +237,15 @@ class Category
 
   def to_json(locale, json : JSON::Builder)
     json.object do
+      json.field "type", "category"
       json.field "title", self.title
-      json.field "contents", self.contents
+      json.field "contents" do
+        json.array do
+          self.contents.each do |item|
+            item.to_json(locale, json)
+          end
+        end
+      end
     end
   end