SPRINGFIELD — Days away from its bimonthly decision on batches of appeals, the state’s top court got a head start this week by agreeing to hear an unusual child custody case.The Illinois Supreme Court on Monday, in a rare move, announced it will look into the case in which a man used a collateral legal attack on a prior conviction to vacate a finding he was an unfit parent.The man, Floyd F., was deemed to have been depraved by a trial judge due to three previous felony convictions and had his parental rights to …