avfilter/vf_datascope: fix heap buffer overflow

Fixes #8309

libavfilter/vf_datascope.c

@@ -973,7 +973,7 @@ static int oscilloscope_filter_frame(AVFilterLink *inlink, AVFrame *frame)
                        frame->width, frame->height,
                        s->ox, s->oy, s->width, s->height + 20 * s->statistics);
 
-    if (s->grid) {
+    if (s->grid && outlink->h >= 10) {
         ff_fill_rectangle(&s->draw, &s->gray, frame->data, frame->linesize,
                           s->ox, s->oy, s->width - 1, 1);