[gnome-themes-standard] Add runtime checks for X11 specific code

[Alexander Larsson <alexl src gnome org>]

commit 9d37a303658a1c2afab42da17c10316bfbba6cc6
Author: Alexander Larsson <alexl redhat com>
Date:   Wed Dec 19 22:08:09 2012 +0100

    Add runtime checks for X11 specific code
    
    This way it works if Gtk+ is built with X11 support, but the active
    backend is something else.

 themes/Adwaita/gtk-3.0/adwaita_engine.c |   17 ++++++++++++-----
 1 files changed, 12 insertions(+), 5 deletions(-)
---
diff --git a/themes/Adwaita/gtk-3.0/adwaita_engine.c b/themes/Adwaita/gtk-3.0/adwaita_engine.c
index f0f48ac..7d9e23d 100644
--- a/themes/Adwaita/gtk-3.0/adwaita_engine.c
+++ b/themes/Adwaita/gtk-3.0/adwaita_engine.c
@@ -121,8 +121,12 @@ adwaita_engine_wm_changed (AdwaitaEngine *self)
 
 #ifdef GDK_WINDOWING_X11
   const gchar *name;
-  name = gdk_x11_screen_get_window_manager_name (gdk_screen_get_default ());
-  is_fallback = (g_strcmp0 (name, "GNOME Shell") != 0);
+  GdkScreen *screen = gdk_screen_get_default ();
+  if (GDK_IS_X11_SCREEN (screen))
+    {
+      name = gdk_x11_screen_get_window_manager_name (screen);
+      is_fallback = (g_strcmp0 (name, "GNOME Shell") != 0);
+    }
 #endif
 
   if (is_fallback)
@@ -153,9 +157,12 @@ adwaita_engine_init (AdwaitaEngine *self)
 #ifdef GDK_WINDOWING_X11
   GdkScreen *screen = gdk_screen_get_default ();
 
-  self->wm_watch_id =
-    g_signal_connect_swapped (screen, "window-manager-changed",
-                              G_CALLBACK (adwaita_engine_wm_changed), self);
+  if (GDK_IS_X11_SCREEN (screen))
+    {
+      self->wm_watch_id =
+	g_signal_connect_swapped (screen, "window-manager-changed",
+				  G_CALLBACK (adwaita_engine_wm_changed), self);
+    }
 #endif
 
   adwaita_engine_wm_changed (self);