executor: skip lock key if lock key is empty (#23188)

[ti-srebot]

cherry-pick #23188 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/24312

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/24312:release-4.0-bdfcaf883e62

---

Signed-off-by: lysu sulifx@gmail.com

What problem does this PR solve?

Issue Number: close #23179

Problem Summary:

e.idxKey may be nil

tidb/executor/point_get.go

Line 226 in 9360d81

err = e.lockKeyIfNeeded(ctx, e.idxKey)

when query condition overflow column's define bound

tidb/executor/point_get.go

Line 444 in 9360d81

return nil, kv.ErrNotExist

then cause panic that described in issue

What is changed and how it works?

Proposal: xxx

What's Changed, How it Works:

add nil check for lockKeyIfNeeded

Related changes

• n/a

Check List

Tests

• Unit test

Side effects

• n/a

Release note

• n/a

---

This change is 

[ti-srebot]

/run-all-tests

[ti-srebot]

@lysu you're already a collaborator in bot's repo.

[coocood]

/lgtm

[lysu]

/run-mybatis-test

[jackysp]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• coocood
• jackysp

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[lysu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: bc1cce4

[zhouqiang-cl]

/merge

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