scale: fix leak occurring when a scale filter is reconfigured

This currently only occurrs in vsrc_buffer in case of mid-stream
size/format change.

Fix trac issue #124.

libavfilter/vf_scale.c

@@ -214,14 +214,18 @@ static int config_props(AVFilterLink *outlink)
 
     scale->input_is_pal = av_pix_fmt_descriptors[inlink->format].flags & PIX_FMT_PAL;
 
-    if(scale->sws)
+    if (scale->sws)
         sws_freeContext(scale->sws);
     scale->sws = sws_getContext(inlink ->w, inlink ->h, inlink ->format,
                                 outlink->w, outlink->h, outlink->format,
                                 scale->flags, NULL, NULL, NULL);
+    if (scale->isws[0])
+        sws_freeContext(scale->isws[0]);
     scale->isws[0] = sws_getContext(inlink ->w, inlink ->h/2, inlink ->format,
                                     outlink->w, outlink->h/2, outlink->format,
                                     scale->flags, NULL, NULL, NULL);
+    if (scale->isws[1])
+        sws_freeContext(scale->isws[1]);
     scale->isws[1] = sws_getContext(inlink ->w, inlink ->h/2, inlink ->format,
                                     outlink->w, outlink->h/2, outlink->format,
                                     scale->flags, NULL, NULL, NULL);