### 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_MAIN_THREAD_GUARD;
	if (use_xr != p_use_xr) {
		use_xr = p_use_xr;
		RS::get_singleton()->viewport_set_use_xr(viewport, use_xr);
		if (!use_xr) {
			
			if (size_allocated) {
				RS::get_singleton()->viewport_set_size(viewport, size.width, size.height);
			} else {
				RS::get_singleton()->viewport_set_size(viewport, 0, 0);
			}
		}
	}
}
bool Viewport::is_using_xr() {