message: fixed union chunk merge build issue
diff: @@ -669,7 +669,10 @@ Status Union(CylonContext *ctx,
  // create final table
  std::shared_ptr<arrow::Table> table = arrow::Table::Make(ltab->schema(), final_data_arrays);
  - table->CombineChunks(ctx->GetMemoryPool(), table);
  + auto merge_status = table->CombineChunks(cylon::ToArrowPool(ctx), &table);
  + if (!merge_status.ok()) {
  + return Status((int) merge_status.code(), merge_status.message());
  + }
  PutTable(dest_id, table);
  return Status::OK();
  }
  