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.
void sspi_SecureHandleFree(SecHandle* handle)
{
	if (!handle)
		return;

	free(handle);
}

void sspi_SecureHandleFree(SecHandle* handle)
{
	if (!handle)
		return;

	free(handle);
}
