Fix a crash in ambient sound biome checking when the player is halfway between level 2 and level 3. Also add API to puzzle chests

This fixes issue https://github.com/FaceDeer/dfcaverns/issues/39

df_caverns/level3.lua

@@ -47,7 +47,12 @@ df_caverns.register_biome_check(function(pos, heat, humidity)
 	end
 	local biome = get_biome(heat, humidity)
 	if biome == "bloodnether" then
-		if subterrane.get_cavern_value("cavern layer 3", pos) < 0 then
+		local cavern_value = subterrane.get_cavern_value("cavern layer 3", pos)
+		if cavern_value == nil then
+			-- this shouldn't happen, the pos.y check above should prevent it.
+			return nil
+		end
+		if cavern_value < 0 then
 			return "nethercap"
 		end
 		return "bloodthorn"

df_caverns/shared.lua

@@ -28,6 +28,7 @@ df_caverns.register_biome_check = function(func)
 	table.insert(get_biome_at_pos_list, func)
 end
 df_caverns.get_biome = function(pos)
+	pos = vector.round(pos)
 	local heat = minetest.get_heat(pos)
 	local humidity = minetest.get_humidity(pos)
 	for _, val in pairs(get_biome_at_pos_list) do

df_caverns/underworld.lua

@@ -17,6 +17,17 @@ if mapgen_helper.log_location_enabled then
 	log_location = mapgen_helper.log_first_location
 end
 
+-- Exposed as a global so that other mods can override it.
+df_caverns.populate_puzzle_chest = function(pos)
+	local meta = minetest.get_meta(pos)
+	local inv = meta:get_inventory()
+	for i = 1, math.random(1,8) do
+		local item = ItemStack(df_underworld_items.colour_items[math.random(1,#df_underworld_items.colour_items)])
+		--item:set_count(math.random(1,4))
+		inv:add_item("main", item)
+	end
+end
+
 local name_pit = function() end
 local name_ruin = function() end
 
@@ -81,8 +92,6 @@ if named_waypoints_path then
 	end
 end
 
-
-
 local c_slade = df_caverns.node_id.slade
 local c_slade_block = df_caverns.node_id.slade_block
 local c_air = df_caverns.node_id.air
@@ -496,13 +505,7 @@ minetest.register_on_generated(function(minp, maxp, seed)
 								if puzzle_chest then
 									local def = minetest.registered_nodes["df_underworld_items:puzzle_chest_closed"]
 									def.can_dig(puzzle_chest) -- initializes the inventory
-									local meta = minetest.get_meta(puzzle_chest)
-									local inv = meta:get_inventory()
-									for i = 1, math.random(1,8) do
-										local item = ItemStack(df_underworld_items.colour_items[math.random(1,#df_underworld_items.colour_items)])
-										--item:set_count(math.random(1,4))
-										inv:add_item("main", item)
-									end
+									df_caverns.populate_puzzle_chest(puzzle_chest)
 								end								
 							end)
 						elseif building.building_type == "medium building" then