They have a captive audience. “Jersey Shore” stars Nicole “Snooki” Polizzi and Jenni “JWoww” Farley are flooded with fan mail — from inmates in prison. “I get a lot of jail letters,” Polizzi, 38, told The Post from the “ Jersey Shore: Family Vacation ” red carpet at Marquee nightclub in Chelsea last week. Nicole “Snooki” Polizzi and Jenni “JWoww” Farley revealed that they receive fan letters from prison inmates. Getty Images for MTV “I read them and I show my husband.” Farley, 41, saves them all — just in case. “I have a file just in case they get out, because it’s not like they went away for taking a car. We’re talking like quadruple homicide, murder, been away since the ’70s,” she said. Angelina Pivarnick also receives shocking messages from fans of the original “ Jersey Shore ,” which ran from 2009 to 2012, and its spinoff, which is airing its ninth and final season on MTV on May 7.…