### 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)

new_rect.position.x = x;
		new_rect.position.y = y;
		new_rect.size.width = event->xconfigure.width;
		new_rect.size.height = event->xconfigure.height;
	}
	if (new_rect == Rect2i(wd.position, wd.size)) {
		return;
	}
	wd.position = new_rect.position;
	wd.size = new_rect.size;
#if defined(VULKAN_ENABLED)
	if (context_vulkan) {
		context_vulkan->window_resize(window_id, wd.size.width, wd.size.height);
	}
#endif
#if defined(GLES3_ENABLED)
	if (gl_manager) {
		gl_manager->window_resize(window_id, wd.size.width, wd.size.height);
	}
#endif
	if (!wd.rect_changed_callback.is_null()) {
		Rect2i r = new_rect;
		Variant rect = r;
		Variant *rectp = &rect;
		Variant ret;
		Callable::CallError ce;
		wd.rect_changed_callback.callp((const Variant **)&rectp, 1, ret, ce);
	}
}
DisplayServer::WindowID DisplayServerX11::_get_focused_window_or_popup() const {