oggparsetheora: fix comment header parsing

Pass the correct header size to ff_vorbis_comment()

Signed-off-by: Martin Storsjö <martin@martin.st>
libtheoraenc: fix granularity of video quality

The floating point version of av_clip has to be used when
converting the quality level.

Signed-off-by: Maximilian Seesslen <mes@seesslen.net>
Signed-off-by: Martin Storsjö <martin@martin.st>