Make screenshot world players invisible

- Prevent them from interfering with each other if
  one machine is used to host the game in "Host
  Server" non-dedicated mode and another is used
  to actually join to take the screenshot.
- Multiple player YCTIWY things shouldn't happen
  anymore.

docs/screenshot-world/.gitignore

@@ -7,6 +7,7 @@ players.*
 players
 groups.txt
 nc_api.template.tr
+nc_api.template.po
 texturepack_override.template.txt
 world.mt
 settingtypes.txt

docs/screenshot-world/worldmods/mocksetup/init.lua

@@ -93,7 +93,9 @@ end
 
 nodecore.register_playerstep({
 		label = "mock hud/fov clear",
-		action = function(player)
+		action = function(player, data)
+			data.properties.visual_size = {x = 0, y = 0}
+
 			nodecore.hud_set(player, {label = "cheats", ttl = 0})
 			nodecore.hud_set(player, {label = "hintcomplete", ttl = 0})