Fix memleak introduced in:

r25185 | stefano | 2010-09-25 03:18:43 +0200 (Sat, 25 Sep 2010) | 1 line

  Make the crop filters accept parametric expressions.

Originally committed as revision 25193 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vf_crop.c

@@ -305,6 +305,7 @@ static void end_frame(AVFilterLink *link)
     CropContext *crop = link->dst->priv;
 
     crop->var_values[N] += 1.0;
+    avfilter_unref_buffer(link->cur_buf);
     avfilter_end_frame(link->dst->outputs[0]);
 }