avfilter/vf_edgedetect: check if height is big enough

Fixes #8260

libavfilter/vf_edgedetect.c

@@ -150,6 +150,7 @@ static void gaussian_blur(AVFilterContext *ctx, int w, int h,
     int i, j;
 
     memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
+    if (h > 1)
         memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
     for (j = 2; j < h - 2; j++) {
         dst[0] = src[0];
@@ -180,7 +181,9 @@ static void gaussian_blur(AVFilterContext *ctx, int w, int h,
         dst += dst_linesize;
         src += src_linesize;
     }
+    if (h > 2)
         memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
+    if (h > 3)
         memcpy(dst, src, w);
 }