libpayload: Don't try to use invalid row count

console->scroll_up() was hanging when console->rows is 0.  This
was happening on delan if no screen was attached.  If there are no
rows, just return.

BUG=b:119234919
TEST=Boot delan with no flat panel.  System boots to OS

Change-Id: Ib022d3c6fc0c9cf360809dca28761a50c787304a
Signed-off-by: Martin Roth <martinroth@chromium.org>
Reviewed-on: https://review.coreboot.org/c/30092
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

payloads/libpayload/drivers/video/video.c

@@ -87,6 +87,9 @@ static void video_console_fixup_cursor(void)
 		cursory++;
 	}
 
+	if (console->rows <= 0)
+		return;
+
 	while(cursory >= console->rows) {
 		console->scroll_up();
 		cursory--;