fix: avoid div by zero and underflow in pitch alloc size guess

[mesutoezdil]

Zero WidthInBytes underflows the size guess to SIZE_MAX, zero ElementSizeBytes divides by zero and crashes. This guards both to 0 before the guess is computed.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of pitched memory allocation requests when the element size or width is zero.
  • Prevented invalid pitch calculations, ensuring memory sizing and out-of-memory tracking remain consistent for these edge cases.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mesutoezdil
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[coderabbitai]

📝 Walkthrough

Walkthrough

cuMemAllocPitch_v2 now sets its pitch guess to zero when ElementSizeBytes or WidthInBytes is zero, changing bytesize and out-of-memory tracking for those cases.

Changes

Pitch validation

Layer / File(s)	Summary
Zero-input pitch guard src/cuda/memory.c	cuMemAllocPitch_v2 avoids division when either input dimension is zero and sets guess_pitch to 0.

Estimated code review effort: 2 (Simple) | ~5 minutes

Suggested reviewers: chaunceyjiang, archlitchi

Poem

A rabbit checked the pitch with care,
Found zero widths hiding there.
No divide now, the guess stays low,
Bytes track safely as they flow.
Hop, hop—edge cases go!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: guarding the pitch allocation size guess against division by zero and underflow.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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