fix decomposition starting level.

leaves now preserve their level when they start decomposing.

mods/bg_tree/decompose.lua

@@ -64,9 +64,8 @@ blockgame.register_increasing_abm({
 		return data.value >= start_decompose_cost
 	end,
 	action = function (pos, node, data)
-		-- NOTE: might wanna access the 4 from somewhere, instead of directly knowing it.
-		-- that way this won't have to change if decomposing leaves max levels change.
-		local level = math.random(1, 4)
+		local def = minetest.registered_nodes[node.name]
+		local level = def.level
 		minetest.set_node(pos, {name = leaves_decomposing .. "_" .. level})
 	end,
 })