Fix nan problem

[songxiaosheng]

What is the purpose of the change?

if window is leave we ignore data
fix #15386

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Make sure gitHub actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 61.00%. Comparing base (a121270) to head (8b2676f).
⚠️ Report is 6 commits behind head on 3.3.

Files with missing lines	Patch %	Lines
...he/dubbo/metrics/aggregate/DubboMergingDigest.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #15586      +/-   ##
============================================
+ Coverage     59.05%   61.00%   +1.95%     
- Complexity       12    11503   +11491     
============================================
  Files          1909     1909              
  Lines         86782    86782              
  Branches      13095    13094       -1     
============================================
+ Hits          51251    52944    +1693     
+ Misses        29989    28417    -1572     
+ Partials       5542     5421     -121     

Flag	Coverage Δ
integration-tests-java21	33.00% <0.00%> (?)
integration-tests-java8	33.05% <0.00%> (?)
samples-tests-java21	31.64% <0.00%> (?)
samples-tests-java8	29.18% <0.00%> (?)
unit-tests-java11	59.07% <0.00%> (-0.03%)	⬇️
unit-tests-java17	58.78% <0.00%> (-0.01%)	⬇️
unit-tests-java21	58.79% <0.00%> (+<0.01%)	⬆️
unit-tests-java8	59.06% <0.00%> (-0.03%)	⬇️

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