### 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)

return size_allocated;
}
Rect2 Viewport::get_visible_rect() const {
	ERR_READ_THREAD_GUARD_V(Rect2());
	Rect2 r;
	if (size == Size2()) {
		r = Rect2(Point2(), DisplayServer::get_singleton()->window_get_size());
	} else {
		r = Rect2(Point2(), size);
	}
	if (size_2d_override != Size2i()) {
		r.size = size_2d_override;
	}
	return r;
}
void Viewport::canvas_parent_mark_dirty(Node *p_node) {
	ERR_MAIN_THREAD_GUARD;
	bool request_update = gui.canvas_parents_with_dirty_order.is_empty();
	gui.canvas_parents_with_dirty_order.insert(p_node->get_instance_id());
	if (request_update) {
		MessageQueue::get_singleton()->push_callable(callable_mp(this, &Viewport::_process_dirty_canvas_parent_orders));
	}
}
void Viewport::_update_audio_listener_2d() {
	if (AudioServer::get_singleton()) {
		AudioServer::get_singleton()->notify_listener_changed();
	}
}
void Viewport::set_as_audio_listener_2d(bool p_enable) {