Fix undefined index and consequential damages in versions code

If the user has no space and there are no versions, there won't be an
`all` index in the versions entry. Hence this triggers a warning and
becomes `null`, afterwards `count`, `foreach` and friends will happily
throw even more warnings and errors because they don't want to play with
`null`. Thus adding a fallback to an empty array.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>