Investigate stat size on Windows

[ruby0x1]

https://github.com/wren-lang/wren-cli/commit/f5f08bbbf5fb96c2e0f092539b0ce39ba1d8263a

Goal is just to validate the intent here. It seems to behave as intended (stat on a directory has no size, unlike unix-likes)

[fermian]

On Windows systems, the Win32 function for getting file size (ie. GetFileSizeEx) always returns zero for directories. Even Wine mimics this behavior.

[joshgoebel]

This looks fair to me unless we're going to start having different tests for different platforms...