avfilter/vf_ciescope: Free out AVFrame on error

Fixes memleak
Fixes part of CID1197065
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_ciescope.c

@@ -1369,8 +1369,10 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 
     if (!s->background) {
         ret = draw_background(ctx);
-        if (ret < 0)
+        if (ret < 0) {
+            av_frame_free(&out);
             return ret;
+        }
         s->background = 1;
     }
     for (y = 0; y < outlink->h; y++) {