Allow to use empty ModelList in Wizard

We might want to execute the wizard on a specific model even without selecting
some of its records

Closes #14291

proteus/proteus/__init__.py

@@ -1242,6 +1242,10 @@ class Wizard(object):
                 ctx['active_id'] = self.models[0].id
                 ctx['active_ids'] = [model.id for model in self.models]
                 ctx['active_model'] = self.models[0].__class__.__name__
+            elif isinstance(self.models, ModelList):
+                ctx['active_id'] = None
+                ctx['active_ids'] = None
+                ctx['active_model'] = self.models.model_name
             else:
                 ctx['active_id'] = None
                 ctx['active_ids'] = None