Misleading balance information in pinewood log production chain.

This is such a low priority that it will never get fixed, but I thought I would report it anyway.

If you are in the economic overview looking at the production chain for pinewood logs, there is an issue when pinewood stumps go to zero. If your chain is balanced and you have enough foresters to keep up with the cutters, the chain will shown green for trees as long as there is at least one stump somewhere on the island. If the stumps go to zero, the trees part of the chain goes to red with a large negative number for tree production. The instant there is at least one stump somewhere on the island, the red turns green again and the negative number becomes a positive number.

This is merely annoying. It does not harm anything -- other than possibly confusing people who thought their pinewood log production chain was balanced. It actually is still balanced. There is probably just an overflow somewhere in the code when tree stumps go to zero.