[llvm] [InferAddressSpaces] Fix null PHI operand when an incoming flat expression is not rewritten (PR #205749)

[Pankaj Dwivedi via llvm-commits]

PankajDwivedi-25 wrote:

This looks similar to one I am working on https://github.com/llvm/llvm-project/pull/215525 unless we agree to consider the above suggestion addressed in PR;https://github.com/llvm/llvm-project/pull/215525 we can move with this.

https://github.com/llvm/llvm-project/pull/205749