[gegl] noise-solid: take care of negative coordinates in permutations table indexing

[Thomas Manni <tmanni src gnome org>]

commit 1563ae38dea6a422eb4c4e53267e617253d12303
Author: Thomas Manni <thomas manni free fr>
Date:   Sat Nov 11 10:50:57 2017 +0100

    noise-solid: take care of negative coordinates in permutations table indexing

 operations/common-gpl3+/noise-solid.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/operations/common-gpl3+/noise-solid.c b/operations/common-gpl3+/noise-solid.c
index 8a35958..f7d8dbd 100644
--- a/operations/common-gpl3+/noise-solid.c
+++ b/operations/common-gpl3+/noise-solid.c
@@ -195,8 +195,8 @@ plain_noise (gdouble         x,
   sum = 0.0;
   x *= s;
   y *= s;
-  a = (gint) floor (x);
-  b = (gint) floor (y);
+  a = (gint) fabs (floor (x));
+  b = (gint) fabs (floor (y));
 
   for (i = 0; i < 2; i++)
     {