loader: lua: disable autoboot timer after password entry

In the lua loader, if one sets a password in loader.conf, the
autoboot_delay timer will start before the menu is displayed. One can
interrupt the autoboot and bring up the menu by entering a keyboard
character before the timer expires.

If this is done a prompt for the password is displayed. Entering the
password will bring up the menu, but the timer will again start and
another keyboard character must be entered or autoboot will abort the
menu and boot the system.

PR: 265472
Reviewed by: kevans
MFC after: 3 days