[llvm] [SimplifyCFG] Fix the compile crash for invalid upper bound value (PR #71351)

[via llvm-commits]

vfdff wrote:

I didn't find an API, which check whether the Upper of return value of computeConstantRange is updated, so I test it with `UpperBound.getZExtValue() != 0`

https://github.com/llvm/llvm-project/pull/71351