Fix LicenseInfo when url is missing

[nichtich]

Current jskos-proxy shows an error at the console:

TpeError: Cannot read properties of undefined (reading 'url')

I guess it's this line when license has no url:

[ { "uri": "http://creativecommons.org/licenses/by-nc-sa/4.0/", "notation": [ "CC BY-NC-SA 4.0" ], "prefLabel": { "de": "Creative Commons Namensnennung, nicht kommerziell, Weitergabe unter gleichen Bedingungen 4.0", "en": "Creative Commons Attribution-NonCommercial-ShareAlike 4.0" } } ]