[clang] [clang][analyzer] Fix a crash in alpha.unix.BlockInCriticalSection (PR #90030)

[Balazs Benics via cfe-commits]

https://github.com/steakhal requested changes to this pull request.

Now the change makes sense. I disagree with the fix though, see inline.

https://github.com/llvm/llvm-project/pull/90030