In Process::ProcessEventData::DoOnRemoval, we need to handle the case where NO thread has a stop reason
specially, and make sure we stop.  This shouldn't happen, but if it does, the user will probably want to
see it.

<rdar://problem/13273125>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@180244 91177308-0d34-0410-b5e6-96231b3b80d8