[gimp] libgimpcolor: Add an assert at start of gimp_render_sub_pixel()

[Mukund Sivaraman <muks src gnome org>]

commit 5b7cd667f21bdad82de6a144dd22d203e4dd7b56
Author: Mukund Sivaraman <muks banu com>
Date:   Thu Oct 13 10:22:32 2011 +0530

    libgimpcolor: Add an assert at start of gimp_render_sub_pixel()
    
    This is to replace the old checks which were removed in
    commit ff6727ae6666a9cc1efeba0f080e9f6124aff520.

 libgimpcolor/gimpadaptivesupersample.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/libgimpcolor/gimpadaptivesupersample.c b/libgimpcolor/gimpadaptivesupersample.c
index 0c79d3d..9317b2f 100644
--- a/libgimpcolor/gimpadaptivesupersample.c
+++ b/libgimpcolor/gimpadaptivesupersample.c
@@ -80,6 +80,8 @@ gimp_render_sub_pixel (gint             max_depth,
   gulong   num_samples = 0;
   gint     cnt;
 
+  g_return_val_if_fail (render_func != NULL, 0);
+
   /* Get offsets for corners */
 
   dx1 = (gdouble) (x1 - sub_pixel_size / 2) / sub_pixel_size;