[CGP] avoid crashing from weightlessness

It's possible that we have branch weights with 0 values.
In that case, don't try to create an impossible BranchProbability.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268935 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed