Justin Timberlake and Ben Affleck have Las Vegas on edge. They are the stars of a new film about the murky world of unauthorized online poker that could cast an unwelcome spotlight on a fledgling legal market that Sin City’s biggest players are betting on. In the movie, Affleck plays an online gambling tycoon in Costa Rica confronted by Timberlake, a graduate student who believes he’s been swindled by the gambling site.