Fix scalar type resolution for optional tensor

[thiagocrepaldi]

When TorchScript Value has an optional tensor, dtype() or scalarType() is not available and raise (by design).

The symbolic _op_with_optional_float_cast must check whether the tensor is otpional or not before calling the scalar type resolution API. This PR fixes that

[pytorch-bot]

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❌ 1 Failures

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NEW FAILURES - The following jobs have failed:

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[thiagocrepaldi]

@pytorch merge -g

[thiagocrepaldi]

@pytorchbot merge -g

[pytorchmergebot]

Merge started

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[pytorchmergebot]

Merge failed

Reason: 2 mandatory check(s) failed (Rule ONNX exporter). The first few are:

• Lint / lintrunner
• Lint / quick-checks

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Raised by workflow job

[shubhambhokare1]

LGTM! Fix lint issues?

[thiagocrepaldi]

@pytorchbot merge -f "Unrelated lint failure: python3: can't open file '/home/runner/work/pytorch/pytorch/.github/scripts/collect_ciflow_labels.py': [Errno 2] No such file or directory"

[pytorchmergebot]

Merge started

Your change will be merged immediately since you used the force (-f) flag, bypassing any CI checks (ETA: 1-5 minutes).

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Questions? Feedback? Please reach out to the PyTorch DevX Team

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