Make humidity ignore ocean chunks.

Just a quick fix to make humidity distributed more evenly among land tiles (currently I suspect a lot of the highest-humidity chunks are underwater, meaning it's not uniform over land and there are probably more big mountainous deserts than big jungles [since humidity is negatively correlated with altitude]).

I also wanted to do the same for temperature, but doing anything with temperature is more annoying because there's a temperature => chaos => altitude dependence chain, and altitude determines whether a tile has ocean or not. If we removed the dependency of chaos on temperature this would be a lot easier.