fix: preserve h2 queue on out-of-order completion

[mcollina]

Fixes: #5404

HTTP/2 streams can complete out of order. The H2 completion path was advancing kRunningIdx and clearing kQueue[kRunningIdx], which assumes in-order completion. When a later stream completed first, this could clear the wrong request slot and leave completed/running entries misclassified. Destroy/error paths could then lose the still-running request or encounter null queue entries.

This changes H2 request finalization to remove the actual completed request from the running queue section, preserving other running requests. It also skips stale null entries defensively in destroy/error cleanup loops.

Tested with:

• node --test test/issue-5404.js
• node --test test/issue-5404.js test/http2-resume-null-request.js test/http2-goaway-retry-body.js test/http2-invalid-session.js
• node --test test/http2-dispatcher.js
• node --test test/issue-5404.js test/http2-pipelining-default.js
• npm run test:h2:core
• npm run lint

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.23%. Comparing base (27586ee) to head (04b4b68).

Files with missing lines	Patch %	Lines
lib/dispatcher/client-h2.js	73.68%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5410      +/-   ##
==========================================
- Coverage   93.24%   93.23%   -0.01%     
==========================================
  Files         110      110              
  Lines       36825    36842      +17     
==========================================
+ Hits        34336    34351      +15     
- Misses       2489     2491       +2     

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