Fix an exception fetching systems when EDSM is disabled
Fix an exception fetching systems when EDSM is disabled

andreaspada/EDDiscovery,klightspeed/EDDiscovery,andreaspada/EDDiscovery,EDDiscovery/EDDiscovery,klightspeed/EDDiscovery,EDDiscovery/EDDiscovery,EDDiscovery/EDDiscovery,klightspeed/EDDiscovery