[llvm] [SandboxVectorizer][NFCI] Fix use of possibly-uninitialized scalar. (PR #122201)

[Tyler Lanphear via llvm-commits]

tylanphear wrote:

@slackito, @vporpo, thank you both for your prompt review. I've modified the patch according to your suggestions to use an opaque ID type. Please let me know how you think the patch looks in its current state.

https://github.com/llvm/llvm-project/pull/122201