Code review submit fails if commits force-pushed to PR: "Start commit oid is not part of the pull request"

[valer-cara]

Describe the bug
Force pushing commits in a PR causes an already open code-review to fail when submitting:
Start commit oid is not part of the pull request

To Reproduce
Steps to reproduce the behavior:

1. Start reviewing a PR: code-review-start
2. Force push a commit in the PR
3. Submit the review: code-review-submit-approve
4. Notice the bug. Submitting the review has failed with an error message: Start commit oid is not part of the pull request.

Expected behavior
I believe there is no feature to cover this use case, but ideally the user would get a notice that the PR content has changed and get an option to Update.

Also, I believe that this situation is a dead end -- I found no way to backup my comments and easily import them in a fresh code-review. I can save the buffer to a file and manually copy/paste the comments to the appropriate locations, but that's difficult.

PS: I wished that the review contents is plain-text so it can easily be tweaked back in place, but i learned that code-review uses a database internally which makes it hard to port existing comments to a fresh code-review instance on the updated PR.

Screenshots
n/a

Desktop (please complete the following information):

• OS: Linux/Manjaro 21.2.5

Additional context
N/A

Thank you! 🙏