CalendarEntryAjax::getValidYearAndMonth

protected function getValidYearAndMonth(int $year, int $month): array
{
	if ($month <= 0)
	{
		return [$year - 1, $month + 12];
	}

	if ($month > 12)
	{
		return [$year + 1, $month - 12];
	}

	return [$year, $month];
}