fix(storage): fix start table key panic when there are only range-tombstones

[Little-Wallace]

I hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

close #8186

Checklist For Contributors

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• I have demonstrated that backward compatibility is not broken by breaking changes and created issues to track deprecated features to be removed in the future. (Please refer to the issue)
• All checks passed in ./risedev check (or alias, ./risedev c)

Checklist For Reviewers

• I have requested macro/micro-benchmarks as this PR can affect performance substantially, and the results are shown.

Documentation

• My PR DOES NOT contain user-facing changes.

Click here for Documentation

Types of user-facing changes

Please keep the types that apply to your changes, and remove the others.

• Installation and deployment
• Connector (sources & sinks)
• SQL commands, functions, and operators
• RisingWave cluster configuration changes
• Other (please specify in the release note below)

Release note

[hzxa21]

Why is this not captured by the daily delete range integration test?

[Little-Wallace]

Why is this not captured by the daily delete range integration test?

It cause that the probability of generate a empty batch with only range-tombstone is too small..

[mergify]

Hey @Little-Wallace, this pull request failed to merge and has been dequeued from the merge train. If you believe your PR failed in the merge train because of a flaky test, requeue it by clicking "Update branch" or pushing an empty commit with git commit --allow-empty -m "rerun" && git push.

[Li0k]

LGTM