### 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)

_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), Point2i());
	const WindowData &wd = windows[p_window];
	if (wd.minimized) {
		return wd.last_pos;
	}
	RECT r;
	if (GetWindowRect(wd.hWnd, &r)) {
		return Point2i(r.left, r.top) - _get_screens_origin();
	}
	return Point2i();
}
void DisplayServerWindows::_update_real_mouse_position(WindowID p_window) {
	ERR_FAIL_COND(!windows.has(p_window));
	POINT mouse_pos;
	if (GetCursorPos(&mouse_pos) && ScreenToClient(windows[p_window].hWnd, &mouse_pos)) {
		if (mouse_pos.x > 0 && mouse_pos.y > 0 && mouse_pos.x <= windows[p_window].width && mouse_pos.y <= windows[p_window].height) {
			old_x = mouse_pos.x;
			old_y = mouse_pos.y;
			old_invalid = false;
			Input::get_singleton()->set_mouse_position(Point2i(mouse_pos.x, mouse_pos.y));
		}
	}
}
void DisplayServerWindows::window_set_position(const Point2i &p_position, WindowID p_window) {