fix(multi-dataset): surface the reserved-column guard, use the name constant

Review on #343:

- buildDatasetsObjects() runs inside the Promise.allSettled(...).then(...)
  chain in onStartParsingFile, which had no .catch. prepareDeleteRecordColumn
  throws on a response carrying the reserved delete-record column, so in this
  flow that became an unhandled rejection: the loop aborted, no dataset was
  parsed and no state was shown. Wrap the call and drop the parse, the way
  fetchDataset's own catch handles a failed getdata.
- The rename-to-Delete? block still used the literal name while the same
  block in editor.component.ts uses DELETE_RECORD_COLUMN_NAME. Use the
  constant here too.

client/src/app/multi-dataset/multi-dataset.component.ts

@@ -22,6 +22,7 @@ import {
   prepareDeleteRecordColumn,
   seedDeleteRecordColumn
 } from '../shared/dc-validator/utils/deleteRecordColumn'
+import { DELETE_RECORD_COLUMN_NAME } from '../shared/dc-validator/utils/deleteRecordColumnRule'
 import { ExcelRule } from '../models/TableData'
 import { HotTableInterface } from '../models/HotTable.interface'
 import { Col } from '../shared/dc-validator/models/col.model'
@@ -364,7 +365,18 @@ export class MultiDatasetComponent implements OnInit, AfterViewInit {
 
       this.uploadLoading = false
 
-      const datasetObjects = this.buildDatasetsObjects(datasets)
+      // buildDatasetsObjects throws when a getdata response carries the
+      // reserved delete-record column (see deleteRecordColumn.ts). This chain
+      // has no .catch, so an uncaught throw here would become an unhandled
+      // rejection that aborts the loop with nothing shown. Log it and drop the
+      // parse, the way fetchDataset's own catch handles a failed getdata.
+      let datasetObjects: DatasetsObject[] = []
+      try {
+        datasetObjects = this.buildDatasetsObjects(datasets)
+      } catch (err) {
+        console.warn('Error building dataset objects', err)
+        return
+      }
 
       datasetObjects.forEach((datasetObject) => {
         this.parsedDatasets.push({
@@ -1107,14 +1119,10 @@ export class MultiDatasetComponent implements OnInit, AfterViewInit {
         datasetObject.headerPks = response.data.sasparams[0].PK.split(' ')
 
         if (
-          datasetObject.headerColumns.indexOf(
-            '_____DELETE__THIS__RECORD_____'
-          ) !== -1
+          datasetObject.headerColumns.indexOf(DELETE_RECORD_COLUMN_NAME) !== -1
         ) {
           datasetObject.headerColumns[
-            datasetObject.headerColumns.indexOf(
-              '_____DELETE__THIS__RECORD_____'
-            )
+            datasetObject.headerColumns.indexOf(DELETE_RECORD_COLUMN_NAME)
           ] = 'Delete?'
         }