[gtk+] wayland: Check the tablet manager before creating a wp_tablet_seat

[Carlos Garnacho <carlosg src gnome org>]

commit 6628ffd686859f7170ea6b8e908a6a805e570e92
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Apr 6 17:29:11 2016 +0200

    wayland: Check the tablet manager before creating a wp_tablet_seat
    
    This makes things non-crashy if the compositor doesn't provide wp_tablet_manager

 gdk/wayland/gdkdevice-wayland.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)
---
diff --git a/gdk/wayland/gdkdevice-wayland.c b/gdk/wayland/gdkdevice-wayland.c
index 4a7d222..15ab038 100644
--- a/gdk/wayland/gdkdevice-wayland.c
+++ b/gdk/wayland/gdkdevice-wayland.c
@@ -3974,11 +3974,14 @@ _gdk_wayland_device_manager_add_seat (GdkDeviceManager *device_manager,
 
   init_devices (seat);
 
-  seat->wp_tablet_seat =
-    zwp_tablet_manager_v1_get_tablet_seat (display_wayland->tablet_manager,
-                                           wl_seat);
-  zwp_tablet_seat_v1_add_listener (seat->wp_tablet_seat, &tablet_seat_listener,
-                                   seat);
+  if (display_wayland->tablet_manager)
+    {
+      seat->wp_tablet_seat =
+        zwp_tablet_manager_v1_get_tablet_seat (display_wayland->tablet_manager,
+                                               wl_seat);
+      zwp_tablet_seat_v1_add_listener (seat->wp_tablet_seat, &tablet_seat_listener,
+                                       seat);
+    }
 
   gdk_display_add_seat (display, GDK_SEAT (seat));
 }