This is a quick fix to PR25838. The issue comes from the restriction that we
cannot normalize probabilities containing both known and unknown ones. A patch
that removes this restriction is under the review now:
http://reviews.llvm.org/D15548
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255867 91177308-0d34-0410-b5e6-96231b3b80d8
