Update YouTubeViewController.m

Because I live in China;I can't access Youtube（Internet Censorship）.I get nothing When I fetch data from link "http://gdata.youtube.com/feeds/api/videos?q=pomplamoose&max-results=50&alt=json", Because ytData is nil,then app crash. error message link to NSJSONSerialization Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'data parameter is nil' on the console..