AVI : Don't free uninitialized ES format descriptor for DV muxed in AVI.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit adeaefc8)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/avi/avi.c

@@ -589,7 +589,10 @@ static int Open( vlc_object_t * p_this )
         if( tk->p_out_muxed == NULL )
             tk->p_es = es_out_Add( p_demux->out, &fmt );
         TAB_APPEND( p_sys->i_track, p_sys->track, tk );
-        es_format_Clean( &fmt );
+        if(!p_sys->b_muxed )
+        {
+            es_format_Clean( &fmt );
+        }
     }
 
     if( p_sys->i_track <= 0 )