[gtk/wip/albfan/offscreen-window] Prevent crashes on gdk wayland implementation using offscreen windows

[Alberto Fanjul <albfan src gnome org>]

commit 83a878185ecc278bc2cf078ad1c19f0162338447
Author: Alberto Fanjul <albertofanjul gmail com>
Date:   Thu Apr 23 11:43:24 2020 +0200

    Prevent crashes on gdk wayland implementation using offscreen windows

 gdk/wayland/gdkwindow-wayland.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index 7a89ece98d..068ac47622 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -2535,6 +2535,8 @@ calculate_moved_to_rect_result (GdkWindow    *window,
                                 gboolean     *flipped_x,
                                 gboolean     *flipped_y)
 {
+  g_return_if_fail (GDK_IS_WAYLAND_WINDOW (window));
+  g_return_if_fail (GDK_IS_WINDOW_IMPL_WAYLAND (window->impl));
   GdkWindowImplWayland *impl = GDK_WINDOW_IMPL_WAYLAND (window->impl);
   GdkWindow *parent;
   gint window_x, window_y;
@@ -5328,6 +5330,8 @@ void
 gdk_wayland_window_restore_shortcuts (GdkWindow *window,
                                       GdkSeat   *gdk_seat)
 {
+  g_return_if_fail (GDK_IS_WAYLAND_WINDOW (window));
+  g_return_if_fail (GDK_IS_WINDOW_IMPL_WAYLAND (window->impl));
   GdkWindowImplWayland *impl = GDK_WINDOW_IMPL_WAYLAND (window->impl);
   struct wl_seat *seat = gdk_wayland_seat_get_wl_seat (gdk_seat);
   struct zwp_keyboard_shortcuts_inhibitor_v1 *inhibitor;