[llvm] [LoopPredication] Fix division by zero in case of zero branch weights (PR #66506)

[Danila Malyutin via llvm-commits]

danilaml wrote:

@dexonsmith I've added a test that would test that zero weights would be treated as if there was no profile, and it also tests scale factor as a byproduct. I left the original test case since I think it's worth having a small reduced regression test for the original issue.

https://github.com/llvm/llvm-project/pull/66506