message: [PoS] read/write block index modifier based on height and not block version.
diff: #ifndef BITCOIN_CHAIN_H
  #define BITCOIN_CHAIN_H
  +#include "chainparams.h"
  #include "pow.h"
  #include "primitives/block.h"
  #include "tinyformat.h"
  @@ -468,10 +469,14 @@ public:
  READWRITE(nMint);
  READWRITE(nMoneySupply);
  READWRITE(nFlags);
  +
  + // v1/v2 modifier selection.
  + if (!Params().IsStakeModifierV2(nHeight)) {
  READWRITE(nStakeModifier);
  - if(this->nVersion > 5) {
  + } else {
  READWRITE(nStakeModifierV2);
  }
  +
  if (IsProofOfStake()) {
  READWRITE(prevoutStake);
  READWRITE(nStakeTime);
  