Fix list group elements

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/events/events.ex

@@ -425,7 +425,7 @@ defmodule Mobilizon.Events do
     |> Page.build_page(page, limit)
   end
 
-  def list_simple_organized_events_for_group(%Actor{} = actor, page, limit) do
+  def list_simple_organized_events_for_group(%Actor{} = actor, page \\ nil, limit \\ nil) do
     list_organized_events_for_group(actor, :all, nil, nil, page, limit)
   end