Fix #7670: Cache the origin tile to prevent recurring calls to the road pathfinder when a vehicle is blocked by another #7822
This is a tentative fix for #7670 , but not fully tested. I thought of caching the origin of where the pathfind starts its search. It seems to solve the issue, but I'm not sure this is the right approach.
Problem is best explained here: #7670 (comment)
savegame for testing, requires only 2 vehicles and a giant road network to trigger the issue : https://github.com/OpenTTD/OpenTTD/files/3801034/2.vehicles.only.zip