### 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_FAIL_NULL(p_control);
	ERR_FAIL_COND(p_control->is_inside_tree());
	ERR_FAIL_COND(p_control->get_parent() != nullptr);
	Control *drag_preview = _gui_get_drag_preview();
	if (drag_preview) {
		memdelete(drag_preview);
	}
	p_control->set_as_top_level(true);
	p_control->set_position(gui.last_mouse_pos);
	p_base->get_root_parent_control()->add_child(p_control); 
	p_control->move_to_front();
	gui.drag_preview_id = p_control->get_instance_id();
}
Control *Viewport::_gui_get_drag_preview() {
	if (gui.drag_preview_id.is_null()) {
		return nullptr;
	} else {
		Control *drag_preview = Object::cast_to<Control>(ObjectDB::get_instance(gui.drag_preview_id));
		if (!drag_preview) {
			ERR_PRINT("Don't free the control set as drag preview.");
			gui.drag_preview_id = ObjectID();
		}
		return drag_preview;
	}
}
void Viewport::_gui_remove_root_control(List<Control *>::Element *RI) {