Ensure chats always get saved to db when _populateChatContent is called

[davidzlu]

Currently, in _populateChatContent, EntryConversations only get saved if the llmResponse is defined:

  const llmResponse = await conversation.getChatContent(
    configId,
    analysis.id,
    messageData.messages[0].message_content,
    conversation.messages
  );

  // If the chat is not empty, update the llm_response
  if (llmResponse) { // FIXME: this will drop chats that fail to get LLM response
    messageData.messages[0].llm_response = llmResponse;
    conversation.messages?.push(messageData.messages[0]);
    await conversation.save();
  }
  return conversation;

The expected behavior should be that user messages should save even if llmResponse fails. Verify bug and fix.