Paul Schrader absentmindedly builds installation art out of seven prescription bottles, two inhalers and an empty martini glass, as we sit in a restaurant for seniors in a Manhattan high-rise. Outside, lights twinkle on the Hudson. In 1975, Schrader went to bed with a pistol under his pillow while writing “Taxi Driver.” “Having the option to end things is the only way I could sleep,” Schrader says.