Added farmlands not buildable

[Former user]

Hi,

if you want to place farmlands in construction mode or the map editor, the area is not able to be builded upon.

WORKAROUND: it seems the farmlands is placed correctly, you have to clear the land after placing the farmland with the shovel tool.

[dalerank]

fixed #941. Farmland now correct builds in constructor mode

→ <<cset f536eb08f3ce>>