Fix bug when 1block dust tx could mitigate difficulty
Fix bug when 1block dust tx could mitigate difficulty

IOCoin/iocoin,IOCoin/iocoin,IOCoin/DIONS,IOCoin/DIONS,IOCoin/DIONS,IOCoin/iocoin,IOCoin/DIONS,IOCoin/iocoin,IOCoin/DIONS,IOCoin/DIONS,IOCoin/DIONS,IOCoin/DIONS,IOCoin/iocoin