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 <kwiberg@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Original-Commit-Position: refs/heads/master@{#19835}
Cr-Mirrored-From: https://webrtc.googlesource.com/src
Cr-Mirrored-Commit: eea063fb955d801f426200a1dbf8608d4981b572
1 file changed