Test edge cases for Cygwin verification

[Nantris]

This code was thrown together pretty quickly and not tested as meticulously as security-related code should be. https://github.com/Flying-Z-Terminal/Flying-Z/blob/master/src/downloadCygwin.mjs

[Nantris]

The Cygwin installer is now signed, which makes the usefulness of the current verification code questionable.