message: fix loading genesis block
diff: @@ -3133,7 +3133,7 @@ bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::P
  bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)
  {
  LOCK(cs_main);
  - return IsBTC16BIPsEnabled(pindexPrev->nTime);
  + return pindexPrev ? IsBTC16BIPsEnabled(pindexPrev->nTime) : false; // pindexPrev == null on genesis block
  }
  // Compute at which vout of the block's coinbase transaction the witness
  