[clang] [clang][ExprConst] Fix crash on uninitialized array subobject (PR #67817)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

I am a bit concerned we don't fully understand how to recover the old diagnostic. I left a comment that I think may help but I think we need to understand this a bit better before committing to a fix.

https://github.com/llvm/llvm-project/pull/67817