Freeciv

cityresult_fill() wants to count value for one another tile in addition to the city center. When it search for the best tile from the city area, unknown and already worked tiles are set to have a value of -1. If there is no other kind of tiles at all, that value of -1 gets used as the value of the best tile. This likely cause other bugs before, but in the end it can trip the assert in the end of the function making sure that total value is positive.