Fix out-of-bounds issue

[apsonawane]

This pull request adds input validation to the segment_sum operator to ensure that segment_ids does not contain negative values and that all values are within the valid range. It also introduces a test to verify that negative segment_ids are correctly rejected.

Input validation improvements:

• Added checks in segment_sum (in operators/math/segment_sum.cc) to return an error if any value in segment_ids is negative, including the first and last elements.
• Added a check to ensure all segment_ids values are within the range [0, last_seg], returning an error if out of bounds.

Testing:

• Added a unit test test_segment_sum_cc_negative_segment_ids in test/test_math_ops.py to verify that the operator raises an exception when segment_ids contains negative values.

[Copilot]

Pull request overview

This pull request strengthens the SegmentSum custom operator by adding runtime input validation for segment_ids to prevent invalid indexing behavior, and adds a regression test to ensure negative segment_ids are rejected.

Changes:

• Add validation in segment_sum to reject negative segment_ids and values outside the computed valid range.
• Add a Python unit test that asserts an error is raised when segment_ids contains a negative value.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
operators/math/segment_sum.cc	Adds segment_ids validation (negative / range) before using values for output indexing.
test/test_math_ops.py	Adds a unit test ensuring negative segment_ids are rejected by the C++ operator.

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