A man holds a photo of Jonathan Diller outside the Queens Courthouse. Stephen Yang for NY Post On Monday, when Queens County Supreme Court Justice Michael Aloise sentenced the killer of NYPD Det. Jonathan Diller to 115 years to life in state prison, he made Diller’s wife Stephanie and son Ryan a solemn vow.  Killer Guy Rivera, he said , “will die in a prison cell, which I promise you he will.”  Queens DA Melinda Katz agreed, saying the decision by the soon-to-retire Aloise — one of the county’s best and most respected jurists — “ensures that this defendant will never be free again to terrorize the streets of New York City.” If only this were certain. In the great state of New York, it is not. Rivera is the kind of defendant for whom prisons are made: a three-time convicted persistent felony offender, a career criminal who murdered one police officer and tried to kill another while possessing two loaded firearms.…