fix(tianmu): fix mysqld crash when exec query limit 0 (#1394)

[adofsauron]

Cause: tianmu engine cannot process this scenario when limit=0 and cannot get conds, resulting in crash
Solution: limit 0 is executed without tianmu

Summary about this PR

Issue Number: close #1394

Tests Check List

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

Changelog

• New Feature
• Bug Fix
• Performance Improvement
• Build/Testing/CI/CD
• Documentation
• Not for changelog (changelog entry is not required)

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features

[mergify]

This pull request's title should follow requirements next. @adofsauron please check it 👇.

Valid format:

fix(vc): fix sth..... (#3306)
  ^         ^---------^  ^----^
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  |         +            +-> you issue id.
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  |         +-> Summary in present tense.
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  +-------> Type: feat, fix, docs, workflow, style, refactor, test, website, chore

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• fix: bug fix for stonedb
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• test: adding missing tests, refactoring tests; no production code change
• website
• chore: updating grunt tasks etc; no production code change

[mergify]

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[konghaiya]

LGTM

[hustjieke]

LGTM

no need