When clearing the priority message queue, don't copy an item to itself.

This avoids a memcpy to overlapping---in this case the same---memory locations.

BUG=4100
R=juberti@webrtc.org, pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33019004

Cr-Commit-Position: refs/heads/master@{#8449}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8449 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed