[0.17.1] Map preview incorrect when editing ribbon world height

[beiju]

Steps to reproduce:

1. Go to Start New Game screen
2. Show preview
3. Select ribbon world preset
4. Under "Advanced", change map height to 80
5. Preview refreshes. The 80 tiles worth of land is rendered correctly. Below it is a black bar of void (as expected), but below that you can still see the land from the previous map. See attachment.

Happens every time, regardless of the order of steps 2 and 3. If you start playing the game, the generated world works correctly.

System: MacOS Mojave 10.14.3, MacBook Pro (Retina, 15-inch, Late 2013)