Allow to disable `Keyboard: Num Lock`

[xfzv]

It would be nice if we could completely disable Keyboard: Num Lock message below the password prompt in combination with XSECURELOCK_SHOW_KEYBOARD_LAYOUT=0.

It works just fine in its current state (the message disappears when disabling num lock and appears when enabling it) but if the user password doesn't contain any character that can be typed from the numeric pad, there's no need to display the numeric pad condition in my opinion.