msvcp140: implement _To_byte

[Stefan Dösinger]

Hi,

I was about to implement this function too, but it seems you've beaten
me by two days :-) .

Am 2017-07-08 um 17:55 schrieb Mikhail Paulyshka:
> +    WCHAR longstr[MAX_PATH + 3];
> +        memset(longstr, 'A', sizeof(longstr));
This memset doesn't do what you probably expect. It doesn't fill the
string with 'A's, but instead with U+4141 characters (䅁,
http://www.fileformat.info/info/unicode/char/4141/index.htm).

> +    if (!src || !dst)
> +        return 0;
This is redundant. WideCharToMultiByte checks this for you and returns
0. I noticed this after sending the _To_wide patch and will send a patch
removing the redundant check from _To_wide.