[goffice] atan2: fix y==-x diagonal case.

[Morten Welinder <mortenw src gnome org>]

commit 7a1ad2b683b2e50a122850ab57a5c1201bcb3a12
Author: Morten Welinder <terra gnome org>
Date:   Tue Feb 11 21:36:00 2014 -0500

    atan2: fix y==-x diagonal case.

 goffice/math/go-quad.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/goffice/math/go-quad.c b/goffice/math/go-quad.c
index db4ecc4..ea1803d 100644
--- a/goffice/math/go-quad.c
+++ b/goffice/math/go-quad.c
@@ -930,7 +930,7 @@ SUFFIX(go_quad_atan2_special) (const QUAD *y, const QUAD *x, DOUBLE *f)
                }
                SUFFIX(go_quad_add) (&d, x, y);
                if (d.h == 0) {
-                       *f = (dy >= 0 ? -0.25 : +0.75);
+                       *f = (dy >= 0 ? +0.75 : -0.25);
                        return TRUE;
                }
        }