fix(activitypub): do not try to calculate timezone from missing geo-coordinates

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

lib/federation/activity_stream/converter/event.ex

@@ -198,6 +198,8 @@ defmodule Mobilizon.Federation.ActivityStream.Converter.Event do
 
   defp calculate_timezone(_object, nil), do: nil
 
+  defp calculate_timezone(_object, %Address{geom: nil}), do: nil
+
   defp calculate_timezone(_object, %Address{geom: geom}) do
     TimezoneDetector.detect(
       nil,