Issue Summary

VSA AI Answers for Email Requests sometimes run into a Fallback Answer Situation. This can be due to lack of KB Articles, ChatGPT Outage, search failures etc. This fallback message fails to Sync with email requests unlike in Portal and HC. This gives the customer impression that not all Issues go through VSA AI Answers flows. 
This is due to the fallback message getting rejected as an empty response in Jira due to it's invalid format. we need to add support for that format of this fallback message.
Context: https://atlassian.slack.com/archives/C092FH6HRMZ/p1752053912201079

Steps to Reproduce

1. Enable Email requests and VSA for Email Requests in a JSM project
2. Send a query to the email id that would trigger fallback (an irrelevant query would work that lacks KB)
3. Assist bot will not respond to that email or in the Jira Issue

Expected Results

Assist Bot should respond with fallback message prompting to retry.

Actual Results

No response from Assist Bot

Workaround

No Workaround curently.