avcodec/cdgraphics: limit scrolling to the line

Fixes: out of array access
Fixes: 47877/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_CDGRAPHICS_fuzzer-5690504626438144

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit b7e30a13)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cdgraphics.c

@@ -239,7 +239,7 @@ static void cdg_scroll(CDGraphicsContext *cc, uint8_t *data,
     for (y = FFMAX(0, vinc); y < FFMIN(CDG_FULL_HEIGHT + vinc, CDG_FULL_HEIGHT); y++)
         memcpy(out + FFMAX(0, hinc) + stride * y,
                in + FFMAX(0, hinc) - hinc + (y - vinc) * stride,
-               FFMIN(stride + hinc, stride));
+               FFABS(stride) - FFABS(hinc));
 
     if (vinc > 0)
         cdg_fill_wrapper(0, 0, out,