### 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)

_update_size_hints(p_window);
	
	XResizeWindow(x11_display, wd.x11_window, size.x, size.y);
	for (int timeout = 0; timeout < 50; ++timeout) {
		XSync(x11_display, False);
		XGetWindowAttributes(x11_display, wd.x11_window, &xwa);
		if (old_w != xwa.width || old_h != xwa.height) {
			break;
		}
		usleep(10000);
	}
	
#if defined(VULKAN_ENABLED)
	if (context_vulkan) {
		context_vulkan->window_resize(p_window, xwa.width, xwa.height);
	}
#endif
#if defined(GLES3_ENABLED)
	if (gl_manager) {
		gl_manager->window_resize(p_window, xwa.width, xwa.height);
	}
#endif
}
Size2i DisplayServerX11::window_get_size(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), Size2i());
	const WindowData &wd = windows[p_window];
	return wd.size;
}
Size2i DisplayServerX11::window_get_size_with_decorations(WindowID p_window) const {