Errors in scanner prepare are not handled

      Status scanner_status;
      HdfsScanner* scanner = CreateAndPrepareScanner(partition, context, &scanner_status);
      if (VLOG_QUERY_IS_ON && (!scanner_status.ok() || scanner == NULL)) {
        stringstream ss;
        ss << "Error preparing text scanner for scan range " << scan_range->file() <<
            "(" << scan_range->offset() << ":" << scan_range->len() << ").";
        ss << endl << runtime_state_->ErrorLog();
        VLOG_QUERY << ss.str();
      }

      status = scanner->ProcessSplit();