Reject configs with ridiculously many channels instead of crashing
Reject configs with ridiculously many channels instead of crashing

We hit this CHECK even though the format wasn't even L16, because we
did the checked_cast before testing the codec name.

BUG=chromium:760994
TBR=ossu@webrtc.org

Change-Id: I382a2f841e51944495500f87650258024030d355
Reviewed-on: https://webrtc-review.googlesource.com/1224
Reviewed-by: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Commit-Queue: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#19835}
TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc