[compiler-rt] [sanitizer] add null check (PR #105612)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

Not sure this is useful. Unable to initialize TLS is a fatal error. The function call requires that the pointer is non-null as well.

https://github.com/llvm/llvm-project/pull/105612