Fix clearing empty chat messages (fixes #3192)

CHANGELOG

@@ -22,7 +22,8 @@ Motions:
 Core:
 - No reload on logoff. OpenSlides is now a full single page
   application [#3172].
-- Adding support for choosing image files as logos.
+- Adding support for choosing image files as logos [#3184].
+- Fixing error when clearing empty chat [#3199].
 
 Users:
 - User without permission to see users can now see agenda item speakers,

openslides/core/views.py

@@ -737,6 +737,7 @@ class ChatMessageViewSet(ModelViewSet):
             args.append(chatmessage.pk)
         chatmessages.delete()
         # Trigger autoupdate and setup response.
+        if len(args) > 0:
             inform_deleted_data(*args)
         return Response({'detail': _('All chat messages deleted successfully.')})