### Godot version

4.0-rc6

### System information

Fedora 37, Mesa Intel ADL GT2

### Issue description

Code that works as expected at runtime fails with Nil references to (assigned) exported vars in the editor:

![tool_global_position_error](https://user-images.githubusercontent.com/364501/222031460-ffb1ecbd-5175-4a42-8470-25285ba5f821.png)


### Steps to reproduce

Try to access the `global_position` of a `Node3D` that's assigned to an exported var.

See that it works at runtime.

See that it errors in the editor with:

> Invalid get index 'global_position' (on base: 'Nil').

### Minimal reproduction project

[tool_test.zip](https://github.com/godotengine/godot/files/10856640/tool_test.zip)

Node *to_node = get_node(p_path);
	if (!Object::cast_to<Viewport>(to_node)) {
		EditorNode::get_singleton()->show_warning(TTR("Selected node is not a Viewport!"));
		return;
	}
	Ref<ViewportTexture> vt;
	vt.instantiate();
	vt->set_viewport_path_in_scene(get_tree()->get_edited_scene_root()->get_path_to(to_node));
	emit_changed(get_edited_property(), vt);
	update_property();
}
void EditorPropertyResource::setup(Object *p_object, const String &p_path, const String &p_base_type) {