You might think nothing would frighten Stephon Marbury more than being an unemployed basketball player. On the contrary. Thursday night, the former Knick drove to Blood Manor, the haunted house on West 27th Street, and sat outside in his Ford Escalade for half an hour, signing autographs, chatting and shaking hands with dozens of people on line. Marbury maintained he was “way too scared” to go inside. And he didn’t — he just enjoyed the spectacle.