avcodec/ffv1enc: update buffer check for 16bps

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 3728603f1854b5c79d1a64dd3b41b80640ef1e7f)

Conflicts:

	libavcodec/ffv1enc.c
(cherry picked from commit c900c6e5c26cd86cf34f9c8d4347cedbd01f3935)
1 file changed