Advanced Rogue 7: fix a crash when casting magic missile. do_zap() dereferenced a struct object pointer while ignoring the result of a NULL check. XRogue had the same problem, though triggering it was unlikely, since XRogue does not include a magic missile spell. Reported by John Harris of @Play.

/*
 * Super-Rogue
 * Copyright (C) 1984 Robert D. Kindelberger
 * All rights reserved.
 *
 * See the file LICENSE.TXT for full copyright and licensing information.
 */

#include	<sgtty.h>
typedef	struct sgttyb	SGTTY;
static SGTTY _tty, _res_flg;