Flood fill solver should work with incomplete MazeMap

[DepthDeluxe]

The maze solving algorithm should work with an incomplete MazeMap to allow for the case when the mapping algorithm can't fully explore the maze. It should consider the unknown areas as filled in with walls. This should be easily implemented with mazemap_does_wall_exist()

[DepthDeluxe]

change FF algorithm so that it performs a BFS on the maze graph. Since this is queue-based, it terminates when the queue is empty. This should allow the flood fill algorithm to run on an incomplete MazeMap.

Next step: testing. Code runs great on full graph but haven't tested it with a partially searched maze.