towards the top of a map there is an issue where the map doesn't load/render properly, making all of the turfs black
test case:
http://files.byondhome.com/RootAbyss/MapLoadingIssue_src.zip
Numbered Steps to Reproduce Problem:
make a decently large map
move to the top of the map
turfs will start to de-render as you move up and down the map
