### 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)

gui.roots.erase(RI);
}
void Viewport::_gui_unfocus_control(Control *p_control) {
	if (gui.key_focus == p_control) {
		gui.key_focus->release_focus();
	}
}
void Viewport::_gui_hide_control(Control *p_control) {
	if (gui.mouse_focus == p_control) {
		_drop_mouse_focus();
	}
	if (gui.key_focus == p_control) {
		gui_release_focus();
	}
	if (gui.mouse_over == p_control) {
		_drop_mouse_over();
	}
	if (gui.drag_mouse_over == p_control) {
		gui.drag_mouse_over = nullptr;
	}
	if (gui.tooltip_control == p_control) {
		_gui_cancel_tooltip();
	}
}
void Viewport::_gui_remove_control(Control *p_control) {