Make code more robust against corrupt database data

tubelib/command.lua

@@ -23,16 +23,20 @@ local function deserialize(s)
 	local tbl = {}
 	for line in s:gmatch("[^;]+") do
 		local num, spos = unpack(string.split(line, "="))
+		if num ~= nil and num ~= "" and spos ~= nil and spos ~= "" then
 			tbl[num] = {pos = minetest.string_to_pos(spos)}
 		end
+	end
 	return tbl
 end
 
 local function serialize(data)
 	local tbl = {}
 	for k,v in pairs(data) do
+		if k ~= nil and k ~= "" and v ~= nil and v.pos ~= nil then
 			tbl[#tbl+1] = k.."="..minetest.pos_to_string(v.pos)
 		end
+	end
 	return table.concat(tbl, ";")
 end