Exit updater out early if a file download fails

[Regisle]

Exit updater out early if a file download fails, this is due to the update not applying anyway if a fail download fails

Other improvements that could be made are:

1. checking the download folder for files downloaded incase a previous download failed or was canceled
   or 2) having it automatically clearing the download folder instead of leaving files there to be overridden

[Wires77]

I think having the other improvements in place would make this a better PR. There's nothing really wrong with this as-is, but the main issue is people entering a download loop in the first place due to shoddy internet, and the updater not using the files it could get to in time.

Then of course we wouldn't want to exit early, in case the first file fails, but the rest are all fine