avfilter/vf_gblur: allow filtering with zero horizontal sigma

libavfilter/vf_gblur.c

@@ -125,7 +125,7 @@ static void gaussianiir2d(AVFilterContext *ctx, int plane)
     const int nb_threads = ff_filter_get_nb_threads(ctx);
     ThreadData td;
 
-    if (s->sigma <= 0 || s->steps < 0)
+    if (s->sigma < 0 || s->steps < 0)
         return;
 
     td.width = width;
@@ -247,7 +247,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         uint16_t *dst16 = (uint16_t *)out->data[plane];
         int y, x;
 
-        if (!s->sigma || !(s->planes & (1 << plane))) {
+        if (!(s->planes & (1 << plane))) {
             if (out != in)
                 av_image_copy_plane(out->data[plane], out->linesize[plane],
                                     in->data[plane], in->linesize[plane],