Fix GetNextTargetRequired function calculating new target value. For every second block after PoS<->FPoS flip nActualSpacing was calculated as a difference between FPoS and PoS blocks (instead of PoS and PoS or FPoS and FPoS) which could lead to too big / too small time difference and wrong difficulty values.
Fix GetNextTargetRequired function calculating new target value. For every second block after PoS<->FPoS flip nActualSpacing was calculated as a difference between FPoS and PoS blocks (instead of PoS and PoS or FPoS and FPoS) which could lead to too big / too small time difference and wrong difficulty values.