fix(tianmu): fix up assert failed on cur_pack != nullptr when using group by on empty temp table (#1912)

[Xinqiangxu]

Summary about this PR

Issue Number: close #1912

Tests Check List

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

Changelog

• [ ] New Feature
• [x] 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

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[Xinqiangxu]

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