Sets the entity onto the next path
in the level if the entity already has a path assigned. Otherwise the entity
is set to the first path in the level.
ENTITY* - entity pointer.
Number of nodes in the path, or 0 is no path was found.
ENTITY* - set onto the next existing
result = path_next(me); // assign My-Entity to the next path
path_set, path_scan, path_nextnode,