[gnome-settings-daemon] wacom: Add guard to _get_area() call

[Bastien Nocera <hadess src gnome org>]

commit 35789150d123ba369522511716150cfb864c9f2b
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Feb 7 14:31:11 2012 +0000

    wacom: Add guard to _get_area() call

 plugins/wacom/gsd-wacom-device.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/plugins/wacom/gsd-wacom-device.c b/plugins/wacom/gsd-wacom-device.c
index 59f366f..6e28995 100644
--- a/plugins/wacom/gsd-wacom-device.c
+++ b/plugins/wacom/gsd-wacom-device.c
@@ -1109,6 +1109,8 @@ gsd_wacom_device_get_area (GsdWacomDevice *device)
 	unsigned char *data = NULL;
 	gint *device_area;
 
+	g_return_val_if_fail (GSD_IS_WACOM_DEVICE (device), NULL);
+
 	g_object_get (device->priv->gdk_device, "device-id", &id, NULL);
 
 	area = XInternAtom (GDK_DISPLAY_XDISPLAY (gdk_display_get_default ()), "Wacom Tablet Area", False);