[clang] [clang][CFG] Fix crash on statement-expression in condition variable (PR #212138)

[Balázs Benics via cfe-commits]

steakhal wrote:

@ojhunt Thank you for your review.
I feel you and I didn't apply enough scrutiny that I would expect from contributors myself.
I apologise for my poor judgment here.

I applied changes but I didn't fully own the product.

https://github.com/llvm/llvm-project/pull/212138