Fix crash in MTG 5.7 logging

Fixes the following error:

AsyncErr: Lua: Runtime error from mod 'cloudlands' in callback environment_OnGenerated(): ...sr/bin/../games/minetest_game/mods/default/functions.lua:731: attempt to call method 'is_player' (a nil value)
stack traceback:
    ...sr/bin/../games/minetest_game/mods/default/functions.lua:731: in function 'log_player_action'
    ...sr/bin/../games/minetest_game/mods/default/functions.lua:753: in function 'on_metadata_inventory_put'
    /home/username/.minetest/mods/cloudlands/cloudlands.lua:2514: in function 'addDetail_secrets'
    /home/username/.minetest/mods/cloudlands/cloudlands.lua:2800: in function 'renderCores'
    /home/username/.minetest/mods/cloudlands/cloudlands.lua:2941: in function </home/username/.minetest/mods/cloudlands/cloudlands.lua:2913>
    ....mount_MineteCbIaBa/usr/bin/../builtin/game/register.lua:446: in function <....mount_MineteCbIaBa/usr/bin/../builtin/game/register.lua:432>

Check if an area is protected before creating a portal there

Use nether.volume_is_natural_and_unprotected() instead of nether.volume_is_natural()

prevent crash when igniting portal

Happens when trying to ignite a portal to the cloudlands, but the cloudlands mod hasn't inited yet because it hasn't needed to generate any islands:

ServerError: AsyncErr: ServerThread::run Lua: Runtime error from mod 'default' in callback item_OnPlace(): ...\minetest-5 latest\bin\..\mods\cloudlands/cloudlands.lua:591: attempt to index upvalue 'noise_heightMap' (a nil value)
stack traceback:
	...\minetest-5 latest\bin\..\mods\cloudlands/cloudlands.lua:591: in function 'is_within_realm'
	...ble)\minetest-5 latest\bin\..\mods\nether/portal_api.lua:1356: in function 'ignite_portal'
	...ble)\minetest-5 latest\bin\..\mods\nether/portal_api.lua:2159: in function <...ble)\minetest-5 latest\bin\..\mods\nether/portal_api.lua:2156>

Prevent half-buried ancient portals being overwritten by landscape

(minor) part of last commit

(minor) fix comments in Portals update

part of previous biomeinfo commit (9939eb9)

Reduce rarity of frozen ponds

Apply dust after decoration

This will cause it to run slower in biomes with dust, due to needing an extra vm:get_data() and vm:set_data(), but prevents the dust nodes from interfering with decorations (e.g. snow preventing tree growth). In native mapgens the dust is applied last, falling on top of the highest nodes.

Lighting update

Prevent shadows from being propagated below islands