Non recoverable error

[Blackclaws]

In general a lot of assumptions about trains staying the same need to go out the window when the LTN surface feature is used now.

Error while running event LtnManager::on_gui_checked_state_changed (ID 3)
LtnManager/scripts/gui/trains.lua:83: attempt to get length of local 'sorted_trains' (a nil value)
stack traceback:
LtnManager/scripts/gui/trains.lua:83: in function 'update'
LtnManager/scripts/gui/index.lua:134: in function 'update'
LtnManager/scripts/gui/index.lua:97: in function 'dispatch'
LtnManager/control.lua:127: in function 'handle_gui_event'
LtnManager/control.lua:136: in function <LtnManager/control.lua:133>
7904.959 Error ServerMultiplayerManager.cpp:92: MultiplayerManager failed: "The mod LTN Manager (0.4.15) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event LtnManager::on_gui_checked_state_changed (ID 3)
LtnManager/scripts/gui/trains.lua:83: attempt to get length of local 'sorted_trains' (a nil value)
stack traceback:
LtnManager/scripts/gui/trains.lua:83: in function 'update'
LtnManager/scripts/gui/index.lua:134: in function 'update'
LtnManager/scripts/gui/index.lua:97: in function 'dispatch'
LtnManager/control.lua:127: in function 'handle_gui_event'
LtnManager/control.lua:136: in function <LtnManager/control.lua:133>"