swaylock: Clear password buffer on Ctrl-C

I've got in the habit of using Ctrl-C with login(1) to restart password entry.
If Sway does the same thing I don't have to retrain my login muscle memory ;)

password.c

@@ -165,6 +165,7 @@ void swaylock_handle_key(struct swaylock_state *state,
 		schedule_indicator_clear(state);
 		schedule_password_clear(state);
 		break;
+	case XKB_KEY_c: /* fallthrough */
 	case XKB_KEY_u:
 		if (state->xkb.control) {
 			clear_password_buffer(&state->password);