fixed handling of network_name

cybersyn/scripts/global.lua

@@ -61,7 +61,7 @@
 ---@field public is_available true?
 ---@field public parked_at_depot_id uint?
 ---@field public depot_name string
----@field public network_name string
+---@field public network_name string? --can only be nil when the train is parked at a depot
 ---@field public network_flag int
 ---@field public priority int
 ---@field public se_depot_surface_i uint --se only

cybersyn/scripts/main.lua

@@ -116,7 +116,7 @@ end
 ---@param train Train
 function remove_available_train(map_data, train_id, train)
 	---@type uint
-	if train.is_available then
+	if train.is_available and train.network_name then
 		local network = map_data.available_trains[train.network_name--[[@as string]]]
 		if network then
 			network[train_id] = nil

cybersyn/scripts/migrations.lua

@@ -154,16 +154,15 @@ local migrations_table = {
 			v.se_is_being_teleported = not v.entity and true or nil
 			--NOTE: we are guessing here because this information was never saved
 			v.se_depot_surface_i = v.entity.front_stock.surface.index
-			if v.parked_at_depot_id then
-				v.is_available = true
+			v.is_available = nil
+			if v.parked_at_depot_id and v.network_name then
 				local network = map_data.available_trains[v.network_name--[[@as string]]]
 				if not network then
 					network = {}
 					map_data.available_trains[v.network_name--[[@as string]]] = network
 				end
 				network[id] = true
-			else
-				v.is_available = nil
+				v.is_available = true
 			end
 		end
 	end,