### 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)

} else {
							is_tooltip_shown = true; 
						}
					} else {
						_gui_cancel_tooltip();
					}
				}
				if (!is_tooltip_shown && over->can_process()) {
					if (gui.tooltip_timer.is_valid()) {
						gui.tooltip_timer->release_connections();
						gui.tooltip_timer = Ref<SceneTreeTimer>();
					}
					gui.tooltip_control = over;
					gui.tooltip_pos = over->get_screen_transform().xform(pos);
					gui.tooltip_timer = get_tree()->create_timer(gui.tooltip_delay);
					gui.tooltip_timer->set_ignore_time_scale(true);
					gui.tooltip_timer->connect("timeout", callable_mp(this, &Viewport::_gui_show_tooltip));
				}
			}
			mm->set_position(pos);
			Control::CursorShape cursor_shape = Control::CURSOR_ARROW;
			{
				Control *c = over;
				Vector2 cpos = pos;
				while (c) {
					if (!gui.mouse_focus_mask.is_empty() || c->has_point(cpos)) {
						cursor_shape = c->get_cursor_shape(cpos);
					} else {
						cursor_shape = Control::CURSOR_ARROW;
					}