[gegl] ff-save: only flush audio if we have an audio stream

[Øyvind Kolås <ok src gnome org>]

commit cd46033446d69713d3d8cf741c48e3ea683bc025
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Nov 27 03:59:41 2015 +0100

    ff-save: only flush audio if we have an audio stream

 operations/external/ff-save.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/operations/external/ff-save.c b/operations/external/ff-save.c
index 2920382..828e32a 100644
--- a/operations/external/ff-save.c
+++ b/operations/external/ff-save.c
@@ -898,6 +898,8 @@ static void flush_audio (GeglProperties *o)
   Priv *p = (Priv*)o->user_data;
 
   int got_packet;
+  if (!p->audio_st)
+    return;
   do
   {
     AVPacket  pkt = { 0 };