FIX: Return next bookmarks page only if it exists (#18139)

It used to return the next URL anyway which lead to an additional
request. On the frontend, if the result set was empty, it kept retrying
until at least one result was returned. This bug is fixed in this commit
too.

app/serializers/user_bookmark_list_serializer.rb

@@ -15,6 +15,6 @@ class UserBookmarkListSerializer < ApplicationSerializer
   end
 
   def include_more_bookmarks_url?
-    @include_more_bookmarks_url ||= object.bookmarks.size == object.per_page
+    @include_more_bookmarks_url ||= object.has_more
   end
 end