crypt() only accepts passwords up to 512 characters (at least in modern libxcrypt >= 4.4.4 like present on EL9)

While we usually do not pass so long passwords into it, there is a situation where we (accidentally) do while using Base64(-Windows) passwords.
This is usually guarded by password_base64_encrypted?, but because we are changing the password, it returns false.
The later code then works fine for the root password, but when we also try to encrypt the grub password, we pass in the (already "encrypted") root password, which now is longer than 512 characters.