[llvm] [llvm] Fix potential null dereference in IR/Verifier (PR #157458)

[Daniel Kuts via llvm-commits]

apach301 wrote:

> So, the check `SP &&` preceding your patch should probably be stripped, as it is dead?

If it cant return nullptr after cast, then yes, I could remove both checks

https://github.com/llvm/llvm-project/pull/157458