Charlie Sheen (left) and his lawyer leave a court hearing. How does Charlie Sheen do it? After a series of wild nights with porn stars and booze, hospital stays, and well-publicized arrests, his employer still has his back. A top exec at CBS said Friday that the network is concerned about Sheen's off-camera behavior, but it hasn't affected his work as the star of television's most popular comedy. "We have a high level of concern," said Nina Tassler, CBS entertainment president. "How can we not?" The actor's recent headlines have included a wild night that left a New York hotel...