- Fix unitialized variable in demux control helper

There's still a segfault somewhere (occurs after many seeks but I can't reproduce it with a debugger)

modules/demux/voc.c

@@ -121,6 +121,8 @@ static int Open( vlc_object_t * p_this )
     date_Init( &p_sys->pts, 1, 1 );
     date_Set( &p_sys->pts, 1 );
 
+    es_format_Init( &p_sys->fmt, AUDIO_ES, 0 );
+
     return VLC_SUCCESS;
 }