Add a comment explaining why we're casting the local
variable.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@217456 91177308-0d34-0410-b5e6-96231b3b80d8
Merge upstream llvm.org r217456 into dev-llgs-local-launch
Eek - a typo slipped in during my test run (those are my tmux key bindings...)