fix bug that SharedQueryBlockInputStream may loss block randomly

[windtalker]

cherry pick #2761 to release-5.0-20210902 branch

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary:

What is changed and how it works?

Proposal: xxx

What's Changed:

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch:

Check List

Tests

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

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[ti-chi-bot]

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[ti-chi-bot]

@windtalker: 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.

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[windtalker]

/rebuild