Town population bug

[DJTB]

Using Alpha 35, I have some towns with a wrong (sometimes even negative)
population.

How to replicate:
- Open a game with some large towns (10.000+) in the Scenario Editor
- Click on the town's name to view its population count
- Save the game and load it as a normal game
- Click on the town's name to view its population count
- Check if the population has decreased (factor 10?)