Fix gss_inquire_cred with no creds
For GSS_Inquire_cred RFC 2743 specifies:
Input:
o cred_handle CREDENTIAL HANDLE -- if GSS_C_NO_CREDENTIAL
-- is specified, default initiator credentials are queried
Thanks to Isaac Boukris for the inital patch on which this one is based.
Fixes: https://fedorahosted.org/gss-ntlmssp/ticket/6