Fail early in static binary script

[dominiklohmann]

There's little more infurating than waiting 30 minutes for CI only for it to say this after the static binary build failed:

ls: cannot access '': No such file or directory
tar: Cowardly refusing to create an empty archive
Try 'tar --help' or 'tar --usage' for more information.

So let's actually fail if something went wrong.

:memo: Checklist

• [x] All user-facing changes have changelog entries.
• [x] The changes are reflected on vast.io, if necessary.
• [x] The PR description contains instructions for the reviewer, if necessary.

:dart: Review Instructions

Watch CI.