[clang] Avoid accessing unset optional, workaround for #100095 (PR #100408)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Can you please add a reference to https://github.com/llvm/llvm-project/issues/100095 in the summary so folks just reading the git log have more context w/o going to the commit itself.

I would like to see a more flushed out long-term plan for fixing this properly but I think it makes sense.

https://github.com/llvm/llvm-project/pull/100408