### 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(false);
	if (!handle_input_locally) {
		ERR_FAIL_COND_V(!is_inside_tree(), false);
		const Viewport *vp = this;
		while (true) {
			if (Object::cast_to<Window>(vp)) {
				break;
			}
			if (!vp->get_parent()) {
				break;
			}
			vp = vp->get_parent()->get_viewport();
		}
		if (vp != this) {
			return vp->is_input_handled();
		}
	}
	return local_input_handled;
}
void Viewport::set_handle_input_locally(bool p_enable) {
	ERR_MAIN_THREAD_GUARD;
	handle_input_locally = p_enable;
}
bool Viewport::is_handling_input_locally() const {