[clang] [analyzer] Fix zext assertion failure in loop unrolling (PR #121203)

[Balazs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

Looks wonderful now.
I had recommended one simplification, but other than that we can merge this.

Thanks again!

https://github.com/llvm/llvm-project/pull/121203