### 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)

Vector2 pos = p_pos;
	String tooltip;
	while (p_control) {
		tooltip = p_control->get_tooltip(pos);
		
		PopupMenu *menu = Object::cast_to<PopupMenu>(this);
		if (menu) {
			tooltip = menu->get_tooltip(pos);
		}
		if (r_tooltip_owner) {
			*r_tooltip_owner = p_control;
		}
		
		if (!tooltip.is_empty()) {
			break;
		}
		
		if (p_control->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
			break;
		}
		if (p_control->is_set_as_top_level()) {
			break;
		}
		
		pos = p_control->get_transform().xform(pos);
		p_control = p_control->get_parent_control();
	}
	return tooltip;
}
void Viewport::_gui_show_tooltip() {