[PDB] Fix another bug in globals stream name lookup.

When we're on the last bucket the computation is tricky.
We were failing when the last bucket contained multiple
matches.  Added a new test for this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344081 91177308-0d34-0410-b5e6-96231b3b80d8