NEW YORK — The zombie apocalypse is headed for New York City. “The Walking Dead” characters Maggie and Negan, played by Lauren Cohan and Jeffrey Dean Morgan, will get a spinoff show called “Isle of the Dead,” set to premiere next year, AMC announced Monday. The six-episode first season will see Maggie and Negan “traveling into a post-apocalyptic Manhattan long ago cut off from the mainland,” the network said. “The crumbling city is filled with the dead and denizens who have made New York City their own world full of anarchy, danger, beauty, and terror,” reads AMC’s description of the show. Des…