message: Fix a segfault when not all writers contributed to a global variable
diff: @@ -683,8 +683,15 @@ static int NeedWriter(FFSArrayRequest Req, int i)
  {
  size_t SelOffset = Req->Start[j];
  size_t SelSize = Req->Count[j];
  - size_t RankOffset = Req->VarRec->PerWriterStart[i][j];
  - size_t RankSize = Req->VarRec->PerWriterCounts[i][j];
  + size_t RankOffset;
  + size_t RankSize;
  + if (Req->VarRec->PerWriterStart[i] == NULL)
  + /* this writer didn't write */
  + {
  + return 0;
  + }
  + RankOffset = Req->VarRec->PerWriterStart[i][j];
  + RankSize = Req->VarRec->PerWriterCounts[i][j];
  if ((SelSize == 0) || (RankSize == 0))
  {
  return 0;
  