### 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)

if (read_only) {
		return;
	}
	const Ref<InputEventMouseMotion> mm = p_ev;
	if (mm.is_valid()) {
		_update_hovered(mm->get_position());
		return;
	}
	const Ref<InputEventMouseButton> mb = p_ev;
	if (mb.is_valid() && mb->get_button_index() == MouseButton::LEFT && mb->is_pressed()) {
		_update_hovered(mb->get_position());
		_update_flag();
	}
	if (mb.is_valid() && mb->get_button_index() == MouseButton::RIGHT && mb->is_pressed()) {
		if (hovered_index >= 0) {
			renamed_layer_index = hovered_index;
			layer_rename->set_position(get_screen_position() + mb->get_position());
			layer_rename->reset_size();
			layer_rename->popup();
		}
	}
}
void EditorPropertyLayersGrid::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_DRAW: {
			Size2 grid_size = get_grid_size();
			grid_size.x = get_size().x;
			flag_rects.clear();