nla: invalidate sec handle after creation

If sec pointer isn't invalidated after creation it is not possible
to check if the upper and lower pointers are valid.

This fixes a segfault in the server part if the client disconnects before
the authentication was finished.
SECURITY_STATUS SEC_ENTRY QueryCredentialsAttributesW(PCredHandle phCredential, ULONG ulAttribute, void* pBuffer)
{
	SEC_WCHAR* Name;
	SECURITY_STATUS status;
	SecurityFunctionTableW* table;

	Name = (SEC_WCHAR*) sspi_SecureHandleGetUpperPointer(phCredential);

	if (!Name)
		return SEC_E_SECPKG_NOT_FOUND;

	table = sspi_GetSecurityFunctionTableWByNameW(Name);

	if (!table)
		return SEC_E_SECPKG_NOT_FOUND;

	if (table->QueryCredentialsAttributesW == NULL)
		return SEC_E_UNSUPPORTED_FUNCTION;

	status = table->QueryCredentialsAttributesW(phCredential, ulAttribute, pBuffer);

	return status;
}

SECURITY_STATUS SEC_ENTRY QueryCredentialsAttributesW(PCredHandle phCredential, ULONG ulAttribute, void* pBuffer)
{
	SEC_WCHAR* Name;
	SECURITY_STATUS status;
	SecurityFunctionTableW* table;

	Name = (SEC_WCHAR*) sspi_SecureHandleGetUpperPointer(phCredential);

	if (!Name)
		return SEC_E_SECPKG_NOT_FOUND;

	table = sspi_GetSecurityFunctionTableWByNameW(Name);

	if (!table)
		return SEC_E_SECPKG_NOT_FOUND;

	if (table->QueryCredentialsAttributesW == NULL)
		return SEC_E_UNSUPPORTED_FUNCTION;

	status = table->QueryCredentialsAttributesW(phCredential, ulAttribute, pBuffer);

	return status;
}
