fix keyboard hotplugging

include/sway/input/keyboard.h

@@ -5,7 +5,6 @@
 
 struct sway_keyboard {
 	struct sway_seat_device *seat_device;
-	struct wl_list link; // sway_seat::keyboards
 
 	struct xkb_keymap *keymap;
 

sway/input/keyboard.c

@@ -103,9 +103,10 @@ void sway_keyboard_configure(struct sway_keyboard *keyboard) {
 }
 
 void sway_keyboard_destroy(struct sway_keyboard *keyboard) {
-	xkb_keymap_unref(keyboard->keymap);
+	if (!keyboard) {
+		return;
+	}
 	wl_list_remove(&keyboard->keyboard_key.link);
 	wl_list_remove(&keyboard->keyboard_modifiers.link);
-	wl_list_remove(&keyboard->link);
 	free(keyboard);
 }