Even when encrypted, can set up opus as the second codec to support the
case of RED interspersed with Opus packets when the RED packet is too
big to fit in one packet.
The change here is to not go through all up stream codecs when trying to
find a match in DownTrack.Bind when source is encrypted. When encrypted,
the down track codec should match the primary upstream codec, i. e. the
codec at index 0.
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