### Godot version

v4.0 rc6

### System information

Windows 10

### Issue description

When using a ViewportTexture from a SubViewport on a TextureRect, it throws errors after running the scene once and then switching scenes in the editor.
![Pasted image 20230227212626](https://user-images.githubusercontent.com/44676282/221680047-984fa03e-33d1-4856-9a7f-1700b28423cf.png)


### Steps to reproduce

Run the canvas-scene once.
Switch to another scene in the editor.
Switch back to the canvas-scene

### Minimal reproduction project

[ViewportTextureError.zip](https://github.com/godotengine/godot/files/10844099/ViewportTextureError.zip)

ERR_READ_THREAD_GUARD_V(Transform2D());
	Transform2D container_transform;
	SubViewportContainer *c = Object::cast_to<SubViewportContainer>(get_parent());
	if (c) {
		if (c->is_stretch_enabled()) {
			container_transform.scale(Vector2(c->get_stretch_shrink(), c->get_stretch_shrink()));
		}
		container_transform = c->get_viewport()->get_screen_transform_internal(p_absolute_position) * c->get_global_transform_with_canvas() * container_transform;
	} else {
		WARN_PRINT_ONCE("SubViewport is not a child of a SubViewportContainer. get_screen_transform doesn't return the actual screen position.");
	}
	return container_transform * get_final_transform();
}
Transform2D SubViewport::get_popup_base_transform() const {
	ERR_READ_THREAD_GUARD_V(Transform2D());
	if (is_embedding_subwindows()) {
		return Transform2D();
	}
	SubViewportContainer *c = Object::cast_to<SubViewportContainer>(get_parent());
	if (!c) {
		return get_final_transform();
	}
	Transform2D container_transform;
	if (c->is_stretch_enabled()) {
		container_transform.scale(Vector2(c->get_stretch_shrink(), c->get_stretch_shrink()));
	}
	return c->get_screen_transform() * container_transform * get_final_transform();
}
bool SubViewport::is_directly_attached_to_screen() const {