Fix NullVideoEngine's CreateChannel implementation.
Fix NullVideoEngine's CreateChannel implementation.

BUG=
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44149004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8980}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc