“A friend said, ‘How do you feel playing all these unflattering characters?’” Melling says. “I don’t think of it in that way.” Photo: Shayan Asgharnia Harry Melling is on the hunt for Box Hill , the book that inspired his gay-biker movie, Pillion . At the Upper West Side outpost of the Strand, the actor is a reedy presence, his small figure buried in a large North Face winter jacket and topped with a shock of curly hair. He’s tracing a finger along the shelves of available fiction in search of