fix: set initial value of fixed-source select fields, if provided

If the initial value provided by the user does not match the field's options, the field's value will be blank (previously, the first option would be selected by default).

src/FormModal.ts

@@ -226,6 +226,7 @@ export class FormModal extends Modal {
                                 fieldInput.options.forEach((option) => {
                                     element.addOption(option.value, option.label);
                                 });
+                                initialValue !== undefined && element.setValue(String(initialValue));
                                 fieldStore.value.set(element.getValue());
                                 element.onChange(fieldStore.value.set);
                             });