[Core] Restore CheckBlock checks before previous block check
[Core] Restore CheckBlock checks before previous block check

in ProcessNewBlock (as it was before nStakeModifierV2) to avoid possible
syncing issues.
Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet