avfilter/af_stereowiden: Check length

Fixes: out of array access
Fixes: tickets/10746/poc13ffmpeg

Found-by: Zeng Yunxiang
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 50f0f8c53c)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_stereowiden.c

@@ -74,6 +74,8 @@ static int config_input(AVFilterLink *inlink)
 
     s->length = s->delay * inlink->sample_rate / 1000;
     s->length *= 2;
+    if (s->length == 0)
+        return AVERROR(EINVAL);
     s->buffer = av_calloc(s->length, sizeof(*s->buffer));
     if (!s->buffer)
         return AVERROR(ENOMEM);