stream: handle falsy push writer fail reasons

[trivikr]

This fixes stream/iter push writer reads after writer.fail() is called
with an explicit falsy reason.

Reads now use the writer state instead of the truthiness of the stored error,
so reasons like 0 and false reject correctly instead of leaving reads
pending.

Fixes: #63568

---

Assisted-by: openai:gpt-5.5

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.34%. Comparing base (b9203ee) to head (5f2ffe5).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/iter/push.js	90.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #63569   +/-   ##
=======================================
  Coverage   90.34%   90.34%           
=======================================
  Files         730      730           
  Lines      234463   234468    +5     
  Branches    43914    43918    +4     
=======================================
+ Hits       211816   211834   +18     
- Misses      14367    14370    +3     
+ Partials     8280     8264   -16     

Files with missing lines	Coverage Δ
lib/internal/streams/iter/push.js	92.06% <90.00%> (+0.05%)	⬆️

... and 26 files with indirect coverage changes

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