Check for undefined value

Author: CarolineDenis

specifyweb/frontend/js_src/lib/components/FormSliders/AttachmentsCollection.tsx

@@ -33,7 +33,7 @@ export function AttachmentsCollection({
   );
 
   const attachmentHasChanged =
-    collection.models.length > 0 && collection.models.at(-1).needsSaved;
+    collection.models.length > 0 && collection.models.at(-1)?.needsSaved;
 
   const attachments: RA<SerializedResource<Attachment>> = React.useMemo(
     () =>