### 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)

if (!is_inside_tree()) {
		return;
	}
	if (!physics_object_picking) {
		return;
	}
	if (Object::cast_to<Window>(this) && Input::get_singleton()->get_mouse_mode() == Input::MOUSE_MODE_CAPTURED) {
		return;
	}
	if (!gui.mouse_in_viewport) {
		
		physics_picking_events.clear();
		return;
	}
	_drop_physics_mouseover(true);