misc/iframe: Fix archive link when there is no snapshot context
When the input SWHID to browse in an iframe does not have any snapshot related qualifiers, the generated link to browse the object in the main archive website was invalid and was leading to HTTP errors.
For instance, in that directory view, clicking on the View in the archive
link leads to a 404 error.
Migrated from D6681 (view on Phabricator)