### 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)

} break;
	}
	switch (p_mode) {
		case WINDOW_MODE_WINDOWED: {
			
		} break;
		case WINDOW_MODE_MINIMIZED: {
			_set_wm_minimized(p_window, true);
		} break;
		case WINDOW_MODE_EXCLUSIVE_FULLSCREEN:
		case WINDOW_MODE_FULLSCREEN: {
			wd.last_position_before_fs = wd.position;
			if (window_get_flag(WINDOW_FLAG_ALWAYS_ON_TOP, p_window)) {
				_set_wm_maximized(p_window, true);
			}
			wd.fullscreen = true;
			if (p_mode == WINDOW_MODE_EXCLUSIVE_FULLSCREEN) {
				wd.exclusive_fullscreen = true;
				_set_wm_fullscreen(p_window, true, true);
			} else {
				wd.exclusive_fullscreen = false;
				_set_wm_fullscreen(p_window, true, false);
			}
		} break;
		case WINDOW_MODE_MAXIMIZED: {
			_set_wm_maximized(p_window, true);
		} break;
	}
}
DisplayServer::WindowMode DisplayServerX11::window_get_mode(WindowID p_window) const {