Casting for the big-screen adaptation of Stephen King’s 1,200-page post-apocalyptic bestseller The Stand is underway, and the franchise has just found its villain. Matthew McConaughey has signed on to star as the creepy cowboy Randall Flagg, who comes to power in Las Vegas after a military-created virus kills most of humanity. Warner Bros. appears to be going all-in on series. The Stand will be released as four separate movies, all telling a different part of the epic story. Josh Boone, who rose to prominence with the Hollywood adaptation of the novel The Fault in Our Stars, has been tapped to direct …