Fix dungeon margin bug

mods/MAPGEN/mcl_dungeons/init.lua

@@ -406,6 +406,8 @@ local function dungeons_nodes(minp, maxp, blockseed)
 	local pr = PseudoRandom(blockseed)
 	for a=1, attempts do
 		local dim = dungeonsizes[pr:next(1, #dungeonsizes)]
+
+		if ymin <= ymax - dim.y - 1 then
 			local x = pr:next(minp.x, maxp.x-dim.x-1)
 			local y = pr:next(ymin  , ymax  -dim.y-1)
 			local z = pr:next(minp.z, maxp.z-dim.z-1)
@@ -415,6 +417,7 @@ local function dungeons_nodes(minp, maxp, blockseed)
 			emerge_area(p1, p2, ecb_spawn_dungeon, {p1=p1, p2=p2, dim=dim, pr=pr})
 		end
 	end
+end
 
 function mcl_dungeons.spawn_dungeon(p1, _, pr)
 	if not p1 or not pr or not p1.x or not p1.y or not p1.z then return end