Fixes a regression from 2c435c0506 - where the support actors must be able to path to the base actor in order to prevent them from spawning in isolated areas. If the base actor is immovable, they cannot path onto it because the base actor blocks them, so no support actors will spawn.
Fix this by allowing the support actors to path back to any cell adjacent to an immovable base actor, rather than requiring them to be able to path to its location directly.
8a56e14d7a