quic: fixup quic stream variable chunk len

[jasnell]

Fixes: #63216

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.03%. Comparing base (facd71e) to head (eafeb01).
⚠️ Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63230      +/-   ##
==========================================
- Coverage   90.04%   90.03%   -0.01%     
==========================================
  Files         713      714       +1     
  Lines      224950   225243     +293     
  Branches    42530    42572      +42     
==========================================
+ Hits       202548   202802     +254     
- Misses      14188    14221      +33     
- Partials     8214     8220       +6     

Files with missing lines	Coverage Δ
lib/internal/quic/quic.js	100.00% <100.00%> (ø)

... and 44 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/73430/ 💛