[clang] Fix null-deref thanks to an attribute on a global declarator chunk (PR #83611)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Note, I opened an issue for this here: https://github.com/llvm/llvm-project/issues/83385

https://github.com/llvm/llvm-project/pull/83611