avfilter/af_rubberband: check if rbs is valid

libavfilter/af_rubberband.c

@@ -157,6 +157,8 @@ static int config_input(AVFilterLink *inlink)
     if (s->rbs)
         rubberband_delete(s->rbs);
     s->rbs = rubberband_new(inlink->sample_rate, inlink->channels, opts, 1. / s->tempo, s->pitch);
+    if (!s->rbs)
+        return AVERROR(ENOMEM);
 
     inlink->partial_buf_size =
     inlink->min_samples =