ZincCloneBundleJob: fixed bug that would prevent a bundle to be downloaded if the folder was there but it was empty

Note: this partially breaks compatibility with empty bundles (which we don't need anymore anyway), but only in the sense that it makes them be downloaded every time.
Merge pull request #31 from mindsnacks/feature/fix-empty-bundle-bug

ZincCloneBundleJob: fixed bug that would prevent a bundle to be downloaded if