Add separator between image and info resources only if DSS is available.

It looks weird if there's a separator between Image Resources and Info
Resources, when there's nothing else between them. So if no DSS
imagery is available, but image / info resources are (eg: for
planets). Like this:

Xplanet (for eg.) >
------------------------
Image Resources >
------------------------
Information Resources >
------------------------

If DSS images are available, things look better:

Angular Distance [ (eg.)
------------------------
Image Resources >
Show DSS Image
Show SDSS Image
------------------------
Information Resources >
------------------------

So, it's best to throw in the separator only when DSS / SDSS links are
shown.