avfilter/af_aderivative: Free out on error

Fixes: CID1197065 Resource leak

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_aderivative.c

@@ -126,6 +126,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         s->prev = ff_get_audio_buffer(inlink, 1);
         if (!s->prev) {
             av_frame_free(&in);
+            av_frame_free(&out);
             return AVERROR(ENOMEM);
         }
     }