For his exhaustive new book on HBO, James Andrew Miller talked to 600 people about the network that brought us “The Sopranos,” “The Wire” and “Veep.” Behind the scenes, executives were playing their own “Game of Thrones.” In the first of a two-part conversation, Miller tells KCRW about his new HBO oral history, “Tinderbox: HBO’s Ruthless Pursuit of New Frontiers.”