[gegl] gegl: make chain parser a bit more resilient

[Øyvind Kolås <ok src gnome org>]

commit 8dc2847b80796d260beda68a3d1a570652637ac0
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Nov 10 18:14:26 2017 +0100

    gegl: make chain parser a bit more resilient
    
    This stops the following from causing a segfault, withotu changing any
    meaningful behavior.
    
    14:46 < tmanni> try: $ gegl input.jpg -o output.png -- threshold aux=]
    14:46 < tmanni> boom

 gegl/gegl-serialize.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gegl/gegl-serialize.c b/gegl/gegl-serialize.c
index d112387..9a5b7da 100644
--- a/gegl/gegl-serialize.c
+++ b/gegl/gegl-serialize.c
@@ -574,7 +574,7 @@ gegl_create_chain_argv (char      **ops,
                       }
                   }
                 g_free (key);
-                if (end_block)
+                if (end_block && level >0)
                   {
                     level--;
                     gegl_node_connect_to (iter[level+1], "output", iter[level],