Handle pan correctly when the terminal is bigger than the window.

tty.c

@@ -746,10 +746,14 @@ tty_window_offset1(struct tty *tty, u_int *ox, u_int *oy, u_int *sx, u_int *sy)
 	*sy = tty->sy - lines;
 
 	if (c->pan_window == w) {
-		if (c->pan_ox + *sx > w->sx)
+		if (*sx >= w->sx)
+			c->pan_ox = 0;
+		else if (c->pan_ox + *sx > w->sx)
 			c->pan_ox = w->sx - *sx;
 		*ox = c->pan_ox;
-		if (c->pan_oy + *sy > w->sy)
+		if (*sy >= w->sy)
+			c->pan_oy = 0;
+		else if (c->pan_oy + *sy > w->sy)
 			c->pan_oy = w->sy - *sy;
 		*oy = c->pan_oy;
 		return (1);