Previously, failure codes were ignored, which meant simulcasted codecs
couldn't e.g. trigger software fallback. This stops the simulcasted
Encode call at the first faiulre and returns that code.
Another option is to continue sending the frame to the other encoders
but still return the first failure code. It's not clear that that is any
better than just quitting as soon as a failure happens.
BUG=
Review-Url: https://codereview.webrtc.org/2008723002
Cr-Commit-Position: refs/heads/master@{#12892}
57779104f0