For anyone holding on to some latent hope that Idris Elba will be the next James Bond, I have some bad news: “ Luther: The Fallen Sun ” puts (another) nail in that very firmly sealed coffin. In one of the rare moments of levity in the sinister film, the embattled detective John Luther sits down at a chic bar and tells the bartender it’s been a long day (an understatement). “I would say a long day calls for a martini,” the bartender says.