Add special loading progress bar.
It should be fast enough to not keep loading screen for noticably long but
will provide better pathfinding for actors inside interior cells.
When distance between start and end point is greater than max radius of area
possibly covered by navmesh there is no way to find path via navmesh. Also if
distance is greater than cell size navmesh might not exists withing mentioned
area because cell is not loaded therefore navmesh is not generated. So minumum
of these values is used to limit max path distance. Assuming that path
actually exists it's possible to build path to the edge of a circle. When
actor reaches initial edge path is built further. However it will not be
optimal.