For MS-CHAP, convert the password from UTF-8 to UCS-2

For MS-CHAP, convert the password from UTF-8 to UCS-2

The MS-CHAPv1 and MS-CHAPv2 RFCs specify that the password is a string
of "Unicode characters", which for Windows means UCS-2; thus the
password could be any even-length string of up to 512 bytes.

Instead of making the incompatible change of requiring the incoming
password to be UCS-2 encoded, assume the password is UTF-8 encoded and
convert it before using it in NtPasswordHash and
EncryptPwBlockWithPasswordHash.

Signed-off-by: Evan Broder <ebroder@mokafive.com>