[CIFS] Fix oops when Windows server sent bad domain name null terminator

Fixes RedHat bug 211672

Windows sends one byte (instead of two) of null to terminate final Unicode
string (domain name) in session setup response in some cases - this caused
cifs to misalign some informational strings (making it hard to convert
from UCS16 to UTF8).

Thanks to Shaggy for his help and Akemi Yagi for debugging/testing

Signed-off-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>