(core) Fixing bug on a fresh Choice and ChoiceList column

Summary: Adding a new element to a new Choice or ChoiceList column resulted in javascript error

Test Plan: Browser tests

Reviewers: georgegevoian, dsagal

Reviewed By: georgegevoian, dsagal

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D2932

app/client/widgets/ChoiceEditor.js

@@ -80,7 +80,7 @@ ChoiceEditor.prototype.prepForSave = async function() {
   const selectedItem = this.autocomplete && this.autocomplete.getSelectedItem();
   if (selectedItem && selectedItem.isNew) {
     const choices = this.options.field.widgetOptionsJson.prop('choices');
-    await choices.saveOnly([...choices.peek(), selectedItem.label]);
+    await choices.saveOnly([...(choices.peek() || []), selectedItem.label]);
   }
 }
 

app/client/widgets/ChoiceListEditor.ts

@@ -157,7 +157,7 @@ export class ChoiceListEditor extends NewBaseEditor {
     const newChoices = tokens.filter(t => t.isNew).map(t => t.label);
     if (newChoices.length > 0) {
       const choices = this.options.field.widgetOptionsJson.prop('choices');
-      await choices.saveOnly([...choices.peek(), ...new Set(newChoices)]);
+      await choices.saveOnly([...(choices.peek() || []), ...new Set(newChoices)]);
     }
   }