bug: set_terrain should ignore flags that are set that it doesn't support

[gynt]

https://github.com/sourcehold/sourcehold-maps/blob/e33d827c2bc90e733f46e62619458f7fe4588e01/sourcehold/tool/memory/map/terrain/init.py#L58

This piece of code writes a very clean logic layer to memory. It overrides what is already there. Instead, it should load everything from memory and just unset things that changed. It should use logic1 to see what is supported to be changed and not touch the rest.