runtime: null-check sizes and dim_order in validateTensorLayout

[vacu9708]

Summary

validateTensorLayout dereferences s_tensor->sizes() and s_tensor->dim_order() without null-checking them first. Both fields are nullable in the schema, and the function is called from Method::parse_external_constants before parseTensor (which does null-check both) runs. Under the default Verification::Minimal, a corrupted .pte/.ptd with either field null causes a SIGSEGV instead of a clean error return.

This PR adds the two missing null guards. Same pattern as #19267 and #17131, which hardened the same function.

Error code: used InvalidExternalData to match the other checks inside validateTensorLayout.

Test result

./test/run_oss_cpp_tests.sh
lintrunner runtime/executor/tensor_parser_exec_aten.cpp \
           runtime/executor/test/tensor_parser_test.cpp

Result: 0 tests failed out of 82. Lint clean.

[pytorch-bot]

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❌ You can merge normally! (2 Unrelated Failures), 1 Unclassified Failure

As of commit fa988fd with merge base acce7cd ():

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• periodic / gather-models (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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