Fix a bug leading to loss of answers for addon-related questions

src/pretix/base/models/orders.py

@@ -769,6 +769,9 @@ class OrderPosition(AbstractPosition):
                     'order_code': order.code
                 })
 
+        # Delete afterwards. Deleting in between might cause deletion of things related to add-ons
+        # due to the deletion cascade.
+        for cartpos in cp:
             cartpos.delete()
         return ops