server: fix memtracker leak with cursor (#44257) | tidb-test=pr/2135

[ti-chi-bot]

This is an automated cherry-pick of #44257

What problem does this PR solve?

Issue Number: close #44254

Problem Summary:

What is changed and how it works?

Detach the memTracker if the resultSet and err are both not empty. Consider the four situations:

1. resultSet == nil && err == nil. It will be detached in the defer of handleNoDelay directly.
2. resultSet != nil && err == nil. It will be detached when the resultSet is closed.
3. resultSet == nil && err != nil. This PR fixes this situations It will be detached right before returning the error.
4. resultSet != nil && err != nil. This PR fixes this situations It will be detached when the resultSet is closed.

Check List

Tests

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

Release note

Fix the issue that the `memTracker` is not cleared when facing an error while executing statement with cursor fetch.

[YangKeao]

LGTM

[ti-chi-bot]

@YangKeao: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

LGTM

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[ti-chi-bot]

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[wshwsh12]

/retest

[wshwsh12]

/retest

[wshwsh12]

/merge

[wshwsh12]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: wshwsh12, XuHuaiyu, YangKeao

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• OWNERS

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[YangKeao]

/cherry-pick release-6.1

[ti-chi-bot]

@YangKeao: new pull request created to branch release-6.1: #44988.

In response to this:

/cherry-pick release-6.1

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