FIxed floating isle generation at chunk boundaries

A mapgen fix authored by paramat, as mentioned here: https://github.com/minetest/minetest/issues/989
Fix spaces float islands code
FIxed floating isle generation at chunk boundaries

A mapgen fix authored by paramat, as mentioned here: https://github.com/minetest/minetest/issues/989
Fix spaces float islands code
randomize values
Merge remote-tracking branch 'upstream/master' into weather