[dconf-editor] Check that backward and forward buttons are different.

[Arnaud Bonatti <arnaudb src gnome org>]

commit 943d1c1d2a64c000b9e8ec18b6a6393285b685f9
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Mon Dec 18 14:06:46 2017 +0100

    Check that backward and forward buttons are different.

 editor/dconf-window.vala |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/editor/dconf-window.vala b/editor/dconf-window.vala
index f664b81..9d53ac5 100644
--- a/editor/dconf-window.vala
+++ b/editor/dconf-window.vala
@@ -428,6 +428,12 @@ class DConfWindow : ApplicationWindow
 
         if (event.button == mouse_back_button)
         {
+            if (mouse_back_button == mouse_forward_button)
+            {
+                warning (_("The same mouse button is set for going backward and forward. Doing nothing."));
+                return false;
+            }
+
             go_backward ((event.state & Gdk.ModifierType.SHIFT_MASK) != 0);
             return true;
         }