codecs: av1: Fix state when we show existing keyframe

Showing existing keyframe have special meaning in AV1. All the references frame will be refreshed with the original keyframe information. The refresh process (7.20) is implemented by saving data from the frame_header into the state. To fix this special case, load all the relevant information into the frame_header. This implements the needed bit of the 7.20 process.

Fixes #1090 (closed)