### 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 (!drag_preview || (c != drag_preview && !drag_preview->is_ancestor_of(c))) {
		return c;
	}
	return nullptr;
}
bool Viewport::_gui_drop(Control *p_at_control, Point2 p_at_pos, bool p_just_check) {
	
	CanvasItem *ci = p_at_control;
	while (ci) {
		Control *control = Object::cast_to<Control>(ci);
		if (control) {
			if (control->can_drop_data(p_at_pos, gui.drag_data)) {
				if (!p_just_check) {
					control->drop_data(p_at_pos, gui.drag_data);
				}
				return true;
			}
			if (control->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
				break;
			}
		}
		p_at_pos = ci->get_transform().xform(p_at_pos);
		if (ci->is_set_as_top_level()) {
			break;
		}
		ci = ci->get_parent_item();
	}
	return false;
}
void Viewport::_gui_input_event(Ref<InputEvent> p_event) {