Fix changing orders when only variants can be changed and no addons

src/pretix/presale/views/order.py

@@ -1392,6 +1392,8 @@ class OrderChange(EventViewMixin, OrderDetailMixin, TemplateView):
             reissue_invoice=True,
         )
 
+        form_valid = True
+        if self.request.event.settings.change_allow_user_addons:
             addons_data = []
             for p in self.positions:
                 if p.addon_to_id or not hasattr(p, 'addon_form'):
@@ -1416,7 +1418,8 @@ class OrderChange(EventViewMixin, OrderDetailMixin, TemplateView):
             except OrderError as e:
                 messages.error(self.request, str(e))
                 form_valid = False
-        else:
+
+        if form_valid:
             form_valid = self._process_change(ocm)
 
         if not form_valid: