The film is set in the far future. Mankind has colonized the stars. On one planet one of the people who helps Riddick is a Muslim. In part of the dialog, the Muslim explains why there still IS an Islam. Supposedly, someone DID nuke Mecca in the past. The Muslim explains that when the mushroom cloud rose into the sky, "the ashes of Mecca were now carried around the whole earth, so now the whole Earth is considered a holy place".
Those who practice Islam, loony as they are, would find a way to justify the continued existence of Islam, despite the loss of their holiest city and center of worship.
RATZ! Back to the old drawing board!