Arg modifier chip list now supports auto complete and arg description as the chip tooltip

Fixed bug that caused custom args to reset after exiting arg modifier without hitting cancel

src/app/settings/settings.component.ts

@@ -144,7 +144,7 @@ export class SettingsComponent implements OnInit {
      }
    });
    dialogRef.afterClosed().subscribe(new_args => {
-    if (new_args !== null) {
+    if (new_args !== null && new_args !== undefined) {
       this.new_config['Downloader']['custom_args'] = new_args;
     }
    });