avcodec/cngdec: Fix integer clipping

Fixes: runtime error: value -36211.7 is outside the range of representable values of type 'short'
Fixes: 2992/clusterfuzz-testcase-6649611793989632

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 51090133b3)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cngdec.c

@@ -146,7 +146,7 @@ static int cng_decode_frame(AVCodecContext *avctx, void *data,
         return ret;
     buf_out = (int16_t *)frame->data[0];
     for (i = 0; i < avctx->frame_size; i++)
-        buf_out[i] = p->filter_out[i + p->order];
+        buf_out[i] = av_clip_int16(p->filter_out[i + p->order]);
     memcpy(p->filter_out, p->filter_out + avctx->frame_size,
            p->order * sizeof(*p->filter_out));