(core) Fix error when filtering empty choice and choice list columns

Summary:
A client error should no longer be thrown when filtering an empty Choice
or Choice List column.

Test Plan: Browser tests.

Reviewers: alexmojaki

Reviewed By: alexmojaki

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3528

app/client/ui/ColumnFilterMenu.ts

@@ -342,7 +342,7 @@ function getEmptyCountMap(fieldOrColumn: ViewFieldRec|ColumnRec): Map<CellValue,
     values = [true, false];
   } else if (['Choice', 'ChoiceList'].includes(columnType)) {
     const options = fieldOrColumn.origCol().widgetOptionsJson;
-    values = options.prop('choices')();
+    values = options.prop('choices')() ?? [];
   }
   return new Map(values.map((v) => [v, {label: String(v), count: 0, displayValue: v}]));
 }