[llvm] [VPlan][Coverity] Fix coverity CID1579964. (PR #121805)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Thanks for the patch! Could you update the description to say what the issue was with the original code and how this patch fixes it? 

I cannot view the covertity link; it asks for a password.

https://github.com/llvm/llvm-project/pull/121805