fix ai-search rewrite query when no search result found

[johnlanni]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.71%. Comparing base (ef31e09) to head (8b481d2).
Report is 374 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1949      +/-   ##
==========================================
+ Coverage   35.91%   43.71%   +7.80%     
==========================================
  Files          69       78       +9     
  Lines       11576    12479     +903     
==========================================
+ Hits         4157     5455    +1298     
+ Misses       7104     6682     -422     
- Partials      315      342      +27     

see 73 files with indirect coverage changes

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