File related functionality bugs: Force having an opened workspace, or support no workspace when running on desktop.

[boltex]

When running on the web, an opened workspace is required for the filesystem to have a 'relative URI' to work from.

When running on desktop, this is not enforced and has many file related command and functionality fail. Either force an opened workspace or properly support not having a workspace opened.

Discovered by @tbpassin in https://github.com/boltex/scripting-samples-leojs/issues/4