[gegl] contrast-curve: opt out of threading

[Øyvind Kolås <ok src gnome org>]

commit 38d75bb9b3d3d50a3255c8337c42c3176d53c37a
Author: Øyvind Kolås <pippin gimp org>
Date:   Thu Oct 12 00:53:57 2017 +0200

    contrast-curve: opt out of threading

 operations/common/contrast-curve.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/operations/common/contrast-curve.c b/operations/common/contrast-curve.c
index 37dcc08..e0e12c6 100644
--- a/operations/common/contrast-curve.c
+++ b/operations/common/contrast-curve.c
@@ -251,6 +251,7 @@ gegl_op_class_init (GeglOpClass *klass)
   point_filter_class->cl_process = cl_process;
   operation_class->prepare = prepare;
   operation_class->opencl_support = TRUE;
+  operation_class->threaded = FALSE; // XXX: recalculate of gegl_curve_calc_value is not thread safe
 
   gegl_operation_class_set_keys (operation_class,
     "name"       , "gegl:contrast-curve",