[release-23.0] Fix bug where query consolidator returns empty result without error when the waiter cap exceeded (#18782)

[vitess-bot]

Description

This is a backport of #18782

[vitess-bot]

Review Checklist

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General

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Backward compatibility

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.70%. Comparing base (58344e1) to head (1bdd44d).
⚠️ Report is 11 commits behind head on release-23.0.

Additional details and impacted files

@@              Coverage Diff              @@
##           release-23.0   #18833   +/-   ##
=============================================
  Coverage         69.70%   69.70%           
=============================================
  Files              1605     1606    +1     
  Lines            214449   214475   +26     
=============================================
+ Hits             149475   149509   +34     
+ Misses            64974    64966    -8     

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