Only use ED for clear screen if at the bottom, same as earlier fix to

clear end of screen.

tty.c

@@ -1218,6 +1218,7 @@ tty_cmd_clearscreen(struct tty *tty, const struct tty_ctx *ctx)
 	tty_margin_off(tty);
 
 	if (tty_pane_full_width(tty, ctx) &&
+	    ctx->yoff + wp->sy >= tty->sy - 1 &&
 	    status_at_line(tty->client) <= 0 &&
 	    tty_term_has(tty->term, TTYC_ED)) {
 		tty_cursor_pane(tty, ctx, 0, 0);