Home free after his sexual assault conviction was overturned, Bill Cosby wants to keep it that way. Lawyers for the actor asked the Supreme Court Monday to reject an appeal from a Pennsylvania prosecutor who wants the higher court to take another look at his criminal sex assault case. The Pennsylvania Supreme Court ruled 4-3 in June to overturn Cosby’s conviction, saying that he was denied a fair trial when Montgomery County District Attorney Risa Vetri Ferman ignored a promise made by her predecessor, Bruce Castor, not to charge him if he agreed to testify in a civil suit brought by his alleg…