avfilter/vf_dctdnoiz: Check threads

Fixes: floating point division by 0
Fixes: Ticket 8269
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_dctdnoiz.c

@@ -564,6 +564,9 @@ static int config_input(AVFilterLink *inlink)
                inlink->h - s->pr_height);
 
     max_slice_h = s->pr_height / ((s->bsize - 1) * 2);
+    if (max_slice_h == 0)
+        return AVERROR(EINVAL);
+
     s->nb_threads = FFMIN3(MAX_THREADS, ff_filter_get_nb_threads(ctx), max_slice_h);
     av_log(ctx, AV_LOG_DEBUG, "threads: [max=%d hmax=%d user=%d] => %d\n",
            MAX_THREADS, max_slice_h, ff_filter_get_nb_threads(ctx), s->nb_threads);