SystemV fix for tty.c

[Bob Esposito]

	Here's my fix for the protection violation trap on a VAX
	in tty.c



	Bob Esposito ... bpa!espo


***** tty.c

/*
 * common ioctl tty code
 */
ttiocom(tp, cmd, arg, mode)
register struct tty *tp;
{
	register flag;
	struct termio cb;
	struct sgttyb tb;
+	extern nulldev();

	switch(cmd) {


                 ------------------------------------------

	case TCSETA:
		if (copyin(arg, &cb, sizeof cb)) {
			u.u_error = EFAULT;
			break;
		}
		if (tp->t_line != cb.c_line) {
			if (cb.c_line < 0 || cb.c_line >= linecnt) {
				u.u_error = EINVAL;
				break;
			}
+			if (linesw[cb.c_line].l_ioctl == nulldev) {
+				u.u_error = EINVAL;
+				break;
+			}

			(*linesw[tp->t_line].l_ioctl)(tp, LDCLOSE, 0, mode);
		}