Fix bug when no rock island groups are configured (#3188)
Fix bug when no rock island groups are configured (#3188)

* Fix bug when no rock island groups are configured

The server would attempt to redefine c.ROCK_ISLAND_GROUPS even if the list was empty, resulting in a 500 error. Checking for truthiness wasn't sufficient, presumably since the list technically has an item in it.

* Use list comprehension to remove falsey values

magfest/ubersystem,magfest/ubersystem,magfest/ubersystem,magfest/ubersystem