[caribou] daemon: Check that we're using the X backend before using it

[Rui Matos <rtcm src gnome org>]

commit e3c26253e53c61d16e17570a76d90bc43da1e5c9
Author: Rui Matos <tiagomatos gmail com>
Date:   Thu Apr 2 19:29:05 2015 +0200

    daemon: Check that we're using the X backend before using it
    
    This won't make us work correctly on other backends but at least we
    won't print criticals anymore.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=747273

 daemon/daemon.vala |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/daemon/daemon.vala b/daemon/daemon.vala
index 59c3869..14c32ad 100644
--- a/daemon/daemon.vala
+++ b/daemon/daemon.vala
@@ -54,7 +54,10 @@ namespace Caribou {
         }
 
         uint32 get_timestamp () {
-            return Gdk.X11Display.get_user_time (display);
+            if (display is Gdk.X11Display)
+                return Gdk.X11Display.get_user_time (display);
+            else
+                return 0;
         }
 
         void set_entry_location (Atspi.Accessible acc) throws Error {