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

[Nikita Popov via llvm-commits]

nikic wrote:

It's probably best to use getUnsignedMax() and then do +1 when assigning TableSize. getUnsignedMax() is the inclusive unsigned upper bound (UINT_MAX for a wrapped range).

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