check for errors in ShadingSystem::ReParameter()

[cmstein]

Description

ShadingSystem() wasn't checking whether the offset returned by interactive_param_offset() was valid or not before performing the ReParameter() memcpy(). So, we could copy data to a location outside of a valid memory block and cause a crash.

Tests

tests pass except for '987 - render-microfacet.opt (Failed)' but I get the same error for main.

Checklist:

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project. If I haven't
  already run clang-format v17 before submitting, I definitely will look at
  the CI test that runs clang-format and fix anything that it highlights as
  being nonconforming.

[lgritz]

Code LGTM, though needs a clang-format and I think you didn't DCO-sign the commit.

[Copilot]

Pull Request Overview

This PR fixes a potential crash in ShadingSystemImpl::ReParameter by checking if the offset returned by interactive_param_offset() is valid before performing a memcpy.

• Added a condition to verify the offset is non-negative
• Prevents the memcpy from executing if the offset is invalid

Comments suppressed due to low confidence (1)

src/liboslexec/shadingsys.cpp:3442

• Returning true when the offset is invalid might be misleading if an invalid offset should indicate a failure. Consider returning false or logging a warning to clearly signal the issue.

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