[zenity] Add a runtime check for X11 (bug #705335)

[Arx Henrique Pereira da Cruz <arxcruz src gnome org>]

commit 58245d4d4acd00e256e29159e645fa0c5f117d34
Author: Benjamin Berg <benjamin sipsolutions net>
Date:   Fri Aug 2 11:17:17 2013 +0200

    Add a runtime check for X11 (bug #705335)
    
    If GTK+ is compiled with multiple backends, then it is necessary
    to do a runtime check for the used backend.

 src/util.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/src/util.c b/src/util.c
index df7317a..a6f2896 100644
--- a/src/util.c
+++ b/src/util.c
@@ -417,8 +417,11 @@ zenity_util_show_dialog (GtkWidget *dialog)
 {
   gtk_widget_realize (dialog);
 #ifdef GDK_WINDOWING_X11
-  g_assert (gtk_widget_get_window(dialog));
-  zenity_util_make_transient (gtk_widget_get_window(dialog));
+  if (GDK_IS_X11_DISPLAY (gdk_display_get_default ()))
+    {
+      g_assert (gtk_widget_get_window(dialog));
+      zenity_util_make_transient (gtk_widget_get_window(dialog));
+    }
 #endif
   gtk_widget_show (dialog);
 }