Fixed checking the length of a null string

in cdk_strlist_add, it would check the strlen of the
'string' parameter before it checked if the parameter was
null.

Signed-off-by Jason Spafford nullprogrammer@gmail.com
xssl compilation fix; patch by Colin Leroy
Ensure failure when no base64 data have been read. Suggested by Ramkumar Chinchani.
doc update