lavfi/vf_dnn_processing.c: fix CID 1460603

CID 1460603 (#1 of 1): Improper use of negative value (NEGATIVE_RETURNS)

libavfilter/vf_dnn_processing.c

@@ -225,6 +225,9 @@ static int copy_uv_planes(DnnProcessingContext *ctx, AVFrame *out, const AVFrame
         uv_height = AV_CEIL_RSHIFT(in->height, desc->log2_chroma_h);
         for (int i = 1; i < 3; ++i) {
             int bytewidth = av_image_get_linesize(in->format, in->width, i);
+            if (bytewidth < 0) {
+                return AVERROR(EINVAL);
+            }
             av_image_copy_plane(out->data[i], out->linesize[i],
                                 in->data[i], in->linesize[i],
                                 bytewidth, uv_height);