dashboard: adapt tile creation to cell base being a concrete class (#17645)

combo/apps/dashboard/templatetags/dashboard.py

@@ -26,6 +26,7 @@ def get_cell_data(cell):
     if cell is None:
         return {}
     cell_data = serializers.serialize('python', [cell])[0]
+    cell_data['fields'].update(serializers.serialize('python', [cell.cellbase_ptr])[0]['fields'])
     del cell_data['pk']
     for key in ('restricted_to_unlogged', 'groups', 'last_update_timestamp',
             'order', 'placeholder', 'public', 'page'):

combo/apps/dashboard/views.py

@@ -59,6 +59,7 @@ class DashboardAddTileView(View):
         if not cell.is_visible(request.user):
             raise PermissionDenied()
         cell.pk = None
+        cell.id = None
         cell.page = dashboard.page
         cell.placeholder = '_dashboard'
         cell.save()