### 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), WINDOW_MODE_WINDOWED);
	const WindowData &wd = windows[p_window];
	if (wd.fullscreen) {
		if (wd.multiwindow_fs) {
			return WINDOW_MODE_FULLSCREEN;
		} else {
			return WINDOW_MODE_EXCLUSIVE_FULLSCREEN;
		}
	} else if (wd.minimized) {
		return WINDOW_MODE_MINIMIZED;
	} else if (wd.maximized) {
		return WINDOW_MODE_MAXIMIZED;
	} else {
		return WINDOW_MODE_WINDOWED;
	}
}
bool DisplayServerWindows::window_is_maximize_allowed(WindowID p_window) const {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND_V(!windows.has(p_window), false);
	
	return true;
}
void DisplayServerWindows::window_set_flag(WindowFlags p_flag, bool p_enabled, WindowID p_window) {