lavfi/ocv: fix build after fd6228e65.
lavfi/ocv: fix crash with no filter name specified.
lavfi/ocv: fix crash with no dilate arguments.
abuffersink: switch from opaque to AVOptions for params

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
buffersink: switch from opaque to AVOptions for params

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>