Panic when extracting entities without loading SavePlugins

[hankjordan]

thread 'main' panicked at 'Requested resource bevy_save::registry::RollbackRegistry does not exist in the `World`.
                Did you forget to add it using `app.insert_resource` / `app.init_resource`?
                Resources are also implicitly added via `app.add_event`,
                and can be added by plugins.',