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

[Balazs Benics via cfe-commits]

https://github.com/steakhal commented:

Thanks for the nice reproducer!
The test looks a bit verbose to my taste, but it's okay as-is.
I had some deeper thoughts of the fix inline to settle before we could merge this.

Thanks again for working on this issue!

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