72 hour visa, from Phnom Penh - Shanghai - Madrid

Hi, I plan to fly to Shanghai from Phnom Penh arriving 0500 on 27/09/14 and will depart for Madrid (via Dubai connection) on 30/09/14 00.05. As this is less than 72 hours and I depart to a different destination from which I arrived, is it correct that I do not need any Chinese visa or to carry out one before my arrival to Shanghai? Thank you.