[clang] [Clang] Fix crash on improper use of __array_extent (PR #94173)

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https://github.com/cor3ntin approved this pull request.

I've edited the title of the PR (which is then used as commit message)
Please follow that style in the future (see also https://llvm.org/docs/DeveloperPolicy.html#commit-messages)

The change itself looks fine, thanks!

https://github.com/llvm/llvm-project/pull/94173