message: validate non null pfrom on blockspamfilter check
diff: @@ -4793,7 +4793,7 @@ bool ProcessNewBlock(CValidationState& state, CNode* pfrom, CBlock* pblock, CDis
  }
  // Store to disk
  - CBlockIndex* pindex = NULL;
  + CBlockIndex* pindex = nullptr;
  bool ret = AcceptBlock (*pblock, state, &pindex, dbp, checked);
  if (pindex && pfrom) {
  mapBlockSource[pindex->GetBlockHash ()] = pfrom->GetId ();
  @@ -4801,7 +4801,7 @@ bool ProcessNewBlock(CValidationState& state, CNode* pfrom, CBlock* pblock, CDis
  CheckBlockIndex ();
  if (!ret) {
  // Check spamming
  - if(GetBoolArg("-blockspamfilter", DEFAULT_BLOCK_SPAM_FILTER)) {
  + if(pfrom && GetBoolArg("-blockspamfilter", DEFAULT_BLOCK_SPAM_FILTER)) {
  CNodeState *nodestate = State(pfrom->GetId());
  nodestate->nodeBlocks.onBlockReceived(pindex->nHeight);
  bool nodeStatus = true;
  