Add validity check on MaxUnpool indicies.

[skottmckay]

Description

Check indices values are valid.

Motivation and Context

Fix invalid write.

[Copilot]

Pull request overview

This pull request adds input validation for MaxUnpool indices to prevent invalid memory writes. The operator now checks that each index is within the valid range [0, output_size) before using it to write to the output tensor, fixing a potential out-of-bounds write vulnerability.

Changes:

• Added bounds checking for indices in MaxUnpool operator to validate they are non-negative and within the output tensor size
• Added test case to verify the operator correctly rejects out-of-bounds indices with a clear error message

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
onnxruntime/core/providers/cpu/nn/Unpool.cc	Added validation to check indices are within bounds [0, output_size) before writing to output tensor, preventing invalid writes
onnxruntime/test/providers/cpu/nn/unpool_op_test.cc	Added test case MaxUnpoolInvalidIndices to verify proper error handling for out-of-bounds indices

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