Fix ~DeltaTree try to delete uninitialized members (#3903)

[ti-chi-bot]

This is an automated cherry-pick of #3903

What problem does this PR solve?

Issue Number: close #3902

Problem Summary:

DeltaIndex try to release uninitialized members.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

Documentation

Release note

Fix the problem of TiFlash crashing when the memory limit is enabled

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JaySon-Huang
• JinheLin

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

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[JinheLin]

/merge

[ti-chi-bot]

@JinheLin: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[ti-chi-bot]

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

Commit hash: 18e35a2