planner: estimation may be negative

[terry1purcell]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

This is copy of issue 55126 - #55126.

A new issue is required because of the cherry pick approval fails due to the prior issue's status being cleared.

2. What did you expect to see? (Required)

Same as 55126

3. What did you see instead (Required)

Same as 55126

4. What is your TiDB version? (Required)

releast 8.1

[terry1purcell]

PR (fix) merged