src: fix console debug output on Windows

The FWrite function on Windows assumed that MultiByteToWideChar
automatically null-terminates the resulting string, but it will only do
so if the size of the source was passed as -1 or null character was
explicitly counted in the size. The FWrite uses std::string and its
`.size()` method which doesn't count the null character even though the
`.data()` method adds it to the resulting string.

https://docs.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-multibytetowidechar#remarks
> MultiByteToWideChar does not null-terminate an output string if the
  input string length is explicitly specified without a terminating null
  character. To null-terminate an output string for this function, the
  application should pass in -1 or explicitly count the terminating null
  character for the input string.

PR-URL: https://github.com/nodejs/node/pull/31580


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>