[gegl] stretch-contrast: Clean up 1st cl_iter on failure

[Daniel Sabo <daniels src gnome org>]

commit bd1f55462e9eb4c3594460ff39cbbed588139893
Author: Daniel Sabo <DanielSabo gmail com>
Date:   Sun Nov 3 14:53:14 2013 -0800

    stretch-contrast: Clean up 1st cl_iter on failure

 operations/common/stretch-contrast.c |   27 ++++++++++++++++-----------
 1 files changed, 16 insertions(+), 11 deletions(-)
---
diff --git a/operations/common/stretch-contrast.c b/operations/common/stretch-contrast.c
index 9094293..8f0b6b3 100644
--- a/operations/common/stretch-contrast.c
+++ b/operations/common/stretch-contrast.c
@@ -319,23 +319,28 @@ cl_process (GeglOperation       *operation,
                                    in_format,
                                    GEGL_CL_BUFFER_READ);
 
-  while (gegl_buffer_cl_iterator_next (i, &err))
+  while (gegl_buffer_cl_iterator_next (i, &err) && !err)
     {
-      if (err) return FALSE;
-
-      err = cl_buffer_get_min_max(i->tex[0],
-                                  i->size[0],
-                                  &i->roi[0],
-                                  &i_min,
-                                  &i_max);
-      if (err) return FALSE;
+      err = cl_buffer_get_min_max (i->tex[0],
+                                   i->size[0],
+                                   &i->roi[0],
+                                   &i_min,
+                                   &i_max);
+      if (err)
+        {
+          gegl_buffer_cl_iterator_stop (i);
+          break;
+        }
 
-      if(i_min < min)
+      if (i_min < min)
         min = i_min;
-      if(i_max > max)
+      if (i_max > max)
         max = i_max;
     }
 
+  if (err)
+    return FALSE;
+
   diff = max-min;
 
   i = gegl_buffer_cl_iterator_new (output,