Fix NPE when intermediary has not released

[IotaBread]

No description provided.

[ghost]

This PR has two main issues:

1. The installer will most likely error out in inexplicable ways because of some 404s, this needs to be properly handled.
2. There is nothing retriggering the build once either intermediary or hashed is published, this needs to be either automatic or at least properly warn (using a Discord webhook or so) the developers so they can watch and manually retrigger a build once they're published

[IotaBread]

The installer will most likely error out in inexplicable ways because of some 404s

How about not listing Minecraft versions without intermediary?

There is nothing retriggering the build once either intermediary or hashed is published

I'm not sure about how that would be fixed here, and it's already a problem without this pr