[clang] Fix false match on nullPointerConstant for array indices (PR #201893)

[Kay Hicketts via cfe-commits]

KHicketts wrote:

> LGTM! Thank you for the fix!

Thanks @AaronBallman  !  I'll do the tidying up.  (I felt compelled to share that I am also a ginger cat owner.  This is Elvis Pretzel who recently featured in a presentation of mine)

<img width="875" height="488" alt="Screenshot 2026-06-30 at 17 45 12" src="https://github.com/user-attachments/assets/5109db5b-4205-4ea6-ae22-3ab81ca347a0" />


https://github.com/llvm/llvm-project/pull/201893