compositor: fix a crash on missing keyboard device

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

src/compositor.c

@@ -1656,17 +1656,20 @@ weston_surface_activate(struct weston_surface *surface,
 {
 	struct weston_compositor *compositor = seat->compositor;
 
+	if (seat->seat.keyboard) {
 		wl_keyboard_set_focus(seat->seat.keyboard, &surface->surface);
 		wl_data_device_set_keyboard_focus(&seat->seat);
 
 		if (seat->seat.keyboard->focus_resource) {
-		wl_keyboard_send_modifiers(seat->seat.keyboard->focus_resource,
+			wl_keyboard_send_modifiers(
+				seat->seat.keyboard->focus_resource,
 				wl_display_next_serial(compositor->wl_display),
 				seat->xkb_state.mods_depressed,
 				seat->xkb_state.mods_latched,
 				seat->xkb_state.mods_locked,
 				seat->xkb_state.group);
 		}
+	}
 
 	wl_signal_emit(&compositor->activate_signal, surface);
 }