The current pbc might be small for an obu frame, so a new pbc is
required then parse this obu frame again. Because
CodedBitstreamAV1Context has already been updated for this obu frame, we
need to restore CodedBitstreamAV1Context, otherwise
CodedBitstreamAV1Context doesn't match this obu frame when parsing obu
frame again, e.g. CodedBitstreamAV1Context.order_hint.

$ ffmpeg -i input.ivf -c:v copy -f null -
[...]
[av1_frame_merge @ 0x558bc3d6f880] ref_order_hint[i] does not match
inferred value: 20, but should be 22.
[av1_frame_merge @ 0x558bc3d6f880] Failed to write unit 1 (type 6).
[av1_frame_merge @ 0x558bc3d6f880] Failed to write packet.
[obu @ 0x558bc3d6e040] av1_frame_merge filter failed to send output
packet
Reviewed-by: James Almer <jamrial@gmail.com>
Reviewed-by: Wenbin Chen <wenbin.chen@intel.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>