don't use (*activeThreads).begin(), use activeThreads->blah().

don't use (*activeThreads).begin(), use activeThreads->blah().
Also don't call (*activeThreads).end() over and over.  Just
call activeThreads->end() once and save the result.
Make sure we always check that there are elements in the list
before we grab the first one.

--HG--
extra : convert_revision : d769d8ed52da99532d57a9bbc93e92ddf22b7e58