### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

mb->set_position(Vector2(old_x, old_y));
			}
			if (uMsg != WM_MOUSEWHEEL && uMsg != WM_MOUSEHWHEEL) {
				if (mb->is_pressed()) {
					if (++pressrc > 0 && mouse_mode != MOUSE_MODE_CAPTURED) {
						SetCapture(hWnd);
					}
				} else {
					if (--pressrc <= 0) {
						if (mouse_mode != MOUSE_MODE_CAPTURED) {
							ReleaseCapture();
						}
						pressrc = 0;
					}
				}
			} else {
				
				POINT coords;
				coords.x = mb->get_position().x;
				coords.y = mb->get_position().y;
				ScreenToClient(hWnd, &coords);
				mb->set_position(Vector2(coords.x, coords.y));
			}
			mb->set_global_position(mb->get_position());
			Input::get_singleton()->parse_input_event(mb);
			if (mb->is_pressed() && mb->get_button_index() >= MouseButton::WHEEL_UP && mb->get_button_index() <= MouseButton::WHEEL_RIGHT) {
				
				Ref<InputEventMouseButton> mbd = mb->duplicate();
				mbd->set_window_id(window_id);
				last_button_state.clear_flag(mouse_button_to_mask(mbd->get_button_index()));