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 90.30%. Comparing base (13feb34) to head (047dd35).

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   90.32%   90.30%   -0.03%     
==========================================
  Files         730      730              
  Lines      234653   234658       +5     
  Branches    43942    43940       -2     
==========================================
- Hits       211959   211911      -48     
- Misses      14415    14482      +67     
+ Partials     8279     8265      -14     

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

... and 46 files with indirect coverage changes

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