free private streamcontext when closing demuxer, fix memory leak, patch by Art Clarke, aclarke at vlideshow dot com

Originally committed as revision 13800 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mov.c

@@ -1899,6 +1899,7 @@ static int mov_read_close(AVFormatContext *s)
         av_freep(&sc->drefs);
         if (sc->pb && sc->pb != s->pb)
             url_fclose(sc->pb);
+        av_freep(&sc);
     }
     if(mov->dv_demux){
         for(i=0; i<mov->dv_fctx->nb_streams; i++){