[Backport 2.x] Fix infinite loop in nested agg

[kkewwei]

Description

Backport 3953557 from #15931

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❕ Gradle check result for bb27833: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.74%. Comparing base (a12e3e6) to head (bb27833).
Report is 7 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...java/org/opensearch/index/mapper/ObjectMapper.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #16075      +/-   ##
============================================
- Coverage     71.75%   71.74%   -0.01%     
- Complexity    64708    64742      +34     
============================================
  Files          5278     5278              
  Lines        302570   302572       +2     
  Branches      44013    44014       +1     
============================================
- Hits         217098   217089       -9     
- Misses        67315    67385      +70     
+ Partials      18157    18098      -59     

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[kkewwei]

@reta, please review when you are free.