### 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)

f->get_buffer((uint8_t *)&data_small.write[0], bytecount_small);
	HICON icon_small = CreateIconFromResource((PBYTE)&data_small.write[0], bytecount_small, TRUE, 0x00030000);
	ERR_FAIL_COND_MSG(!icon_small, "Could not create 16x16 @" + itos(small_icon_cc) + " icon, error: " + format_error_message(GetLastError()) + ".");
	
	int err = 0;
	SetLastError(err);
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_SMALL, (LPARAM)icon_small);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_SMALL: " + format_error_message(err) + ".");
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_BIG, (LPARAM)icon_big);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_BIG: " + format_error_message(err) + ".");
	memdelete(icon_dir);
}
void DisplayServerWindows::set_icon(const Ref<Image> &p_icon) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!p_icon.is_valid());
	if (icon != p_icon) {
		icon = p_icon->duplicate();
		if (icon->get_format() != Image::FORMAT_RGBA8) {
			icon->convert(Image::FORMAT_RGBA8);
		}
	}
	int w = icon->get_width();
	int h = icon->get_height();
	
	int icon_len = 40 + h * w * 4;
	Vector<BYTE> v;
	v.resize(icon_len);
	BYTE *icon_bmp = v.ptrw();