Fix an issue that Simon pointed out to me on IRC. There were cases in the

Fix an issue that Simon pointed out to me on IRC.  There were cases in the
trunk version of find_idle_thread() where the old full frame processing
information was not cleared out.  This would have caused full frames to get
deferred for processing by threads that weren't actually processing frames for
that call.  Nice catch!!

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@77941 65c4cc65-6c06-0410-ace0-fbb531ad65f3