gh-35291: do not evaluate unnecessarily

    
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### 📚 Description

Currently, `Stream_cauchy_compose` unnecessarily evaluates its right
argument `g` (implicitly), even if the corresponding coefficient of the
left argument `f` is zero.  This breaks various recursive definitions.


Fixes #35261.

### 📝 Checklist

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### ⌛ Dependencies
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URL: #35291
Reported by: Martin Rubey
Reviewer(s): Travis Scrimshaw