Check the number of playout channels instead of the send channels in StopPlayout()

BUG=2467
R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2420004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4989 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed