No good deed goes unpunished.Faced with evidence that a man had been wrongfully convicted in the slaying of a 7-year-old girl, then-DeKalb County State’s Attorney Richard H. Schmack could have brushed the matter aside and avoided the political fallout.Instead, he personally combed through piles of court files, investigators’ reports and trial and grand jury transcripts to determine whether Jack McCullough was innocent of the 1957 crime.Concluding it was physically impossible for McCullough to have been in …