Allow non-players to dig locked chests.

mods/default/nodes.lua

@@ -1410,7 +1410,11 @@ local function get_locked_chest_formspec(pos)
 end
 
 local function has_locked_chest_privilege(meta, player)
-	if player:get_player_name() ~= meta:get_string("owner") then
+	local name = ""
+	if player then
+		name = player:get_player_name()
+	end
+	if name ~= meta:get_string("owner") then
 		return false
 	end
 	return true