FIX #18940 TIME 0:10 Attachment cannot be previewed

src/frontend/app/viewer/document-viewer.component.ts

@@ -182,6 +182,9 @@ export class DocumentViewerComponent implements OnInit, OnDestroy {
     }
 
     ngOnInit() {
+        if (this.downloadActions === undefined) {
+            this.downloadActions = [];
+        }
         this.setEditor();
 
         this.http.get('../rest/indexing/fileInformations').pipe(