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 AcquireCredentialsHandleA(SEC_CHAR* pszPrincipal, SEC_CHAR* pszPackage,
		ULONG fCredentialUse, void* pvLogonID, void* pAuthData, SEC_GET_KEY_FN pGetKeyFn,
		void* pvGetKeyArgument, PCredHandle phCredential, PTimeStamp ptsExpiry)
{
	SECURITY_STATUS status;
	SecurityFunctionTableA* table = sspi_GetSecurityFunctionTableAByNameA(pszPackage);

	if (!table)
		return SEC_E_SECPKG_NOT_FOUND;

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

	status = table->AcquireCredentialsHandleA(pszPrincipal, pszPackage, fCredentialUse,
			pvLogonID, pAuthData, pGetKeyFn, pvGetKeyArgument, phCredential, ptsExpiry);

	return status;
}

SECURITY_STATUS SEC_ENTRY AcquireCredentialsHandleA(SEC_CHAR* pszPrincipal, SEC_CHAR* pszPackage,
		ULONG fCredentialUse, void* pvLogonID, void* pAuthData, SEC_GET_KEY_FN pGetKeyFn,
		void* pvGetKeyArgument, PCredHandle phCredential, PTimeStamp ptsExpiry)
{
	SECURITY_STATUS status;
	SecurityFunctionTableA* table = sspi_GetSecurityFunctionTableAByNameA(pszPackage);

	if (!table)
		return SEC_E_SECPKG_NOT_FOUND;

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

	status = table->AcquireCredentialsHandleA(pszPrincipal, pszPackage, fCredentialUse,
			pvLogonID, pAuthData, pGetKeyFn, pvGetKeyArgument, phCredential, ptsExpiry);

	return status;
}
