fix: ensure topic is created if not found in loadTopicMessagesThunk

* Added logic to create a new topic with an empty messages array if the specified topic does not exist in the database.

src/renderer/src/store/thunk/messageThunk.ts

@@ -721,6 +721,11 @@ export const loadTopicMessagesThunk =
 
     try {
       const topic = await db.topics.get(topicId)
+
+      if (!topic) {
+        await db.topics.add({ id: topicId, messages: [] })
+      }
+
       const messagesFromDB = topic?.messages || []
 
       if (messagesFromDB.length > 0) {