winscard: add stubs for SCardListReadersA/W (try 3)

[Nikolay Sivov]

> +LONG WINAPI SCardListReadersA(SCARDCONTEXT context, const CHAR *groups, char *readers, DWORD *buflen)
> +{
> +    FIXME("(%lx, %s, %s, %p) stub\n", context, debugstr_a(groups), debugstr_a(readers), buflen);
> +    return SCARD_F_INTERNAL_ERROR;
> +}
> +
> +LONG WINAPI SCardListReadersW(SCARDCONTEXT context, const WCHAR *groups, WCHAR *readers, DWORD *buflen)
> +{
> +    FIXME("(%lx, %s, %s, %p) stub\n", context, debugstr_w(groups), debugstr_w(readers), buflen);
> +    return SCARD_F_INTERNAL_ERROR;
> +}

'readers' is an out buffer.