Return msg in readLoop of receiver (#3465)

[ti-chi-bot]

This is an automated cherry-pick of #3465

What problem does this PR solve?

Issue Number: close #3444

Problem Summary: if the first read fails, this for(,,) may retry later, so recv_msg should be returned.

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

Side effects

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• fzhedu
• windtalker

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All committers have signed the CLA.

[windtalker]

LGTM

[fzhedu]

LGTM

[fzhedu]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 0cbf956

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