Actor Hugh Laurie has left the sanitized American hospital of his TV series “House MD” and burrowed deep into shadowy British mystery. He has not only adapted one of Agatha Christie’s classic murder stories, but is directing “Why Didn’t They Ask Evans?” arriving on BritBox April 12. He says he was talking with the Christie estate about playing a role in another of her works when something weird happened. “I probably shouldn’t say which one it is because … they’ve probably gone to Colin Firth now, let’s be honest,” he says. “But in the course of that conversation, I just happened to mention ‘…