get_random_location_from_navigation() returns None for Custom map

[JoseZF]

I got the same warning when trying to create the navigation file for a custom map and when trying to run generate_traffic.py (only pedestrians) in the same map. The function to get a random location from navigation returns None and therefore it cannot create a spawn point for pedestrians. I am not sure whether the error is related to the warning but it seems to be. Windows 10, Carla 9.13

Originally posted by @JoseZF in https://github.com/carla-simulator/carla/issues/2766#issuecomment-1214859371