XSECURELOCK_WANT_FIRST_KEYPRESS: no longer forward the first keypress if it is...

XSECURELOCK_WANT_FIRST_KEYPRESS: no longer forward the first keypress if it is purely control characters.

Fixes "trying to unlock with the escape key only causes the screen to
quickly turn on and off again", as well as "immediate authentication
failure when trying to unlock with the enter key".

Internal reference: b/72708660.