Visual Signals crashing in multiplayer

[Zomis]

• New player joining
• New player didn't see the GUI button at the top so I placed down a GUI Signal Display
• New player clicked the GUI button at the top and clicked one of the checkboxes

Crash:

603005.674 Error MainLoop.cpp:1207: Exception at tick 19555041: The mod Visual Signals (0.18.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event visual-signals::on_gui_checked_state_changed (ID 3)
__visual-signals__/control.lua:212: attempt to index field 'gui_signal_display' (a nil value)
stack traceback:
        __visual-signals__/control.lua:212: in function <__visual-signals__/control.lua:205>
603005.675 Error ServerMultiplayerManager.cpp:90: MultiplayerManager failed: "The mod Visual Signals (0.18.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event visual-signals::on_gui_checked_state_changed (ID 3)
__visual-signals__/control.lua:212: attempt to index field 'gui_signal_display' (a nil value)
stack traceback:
        __visual-signals__/control.lua:212: in function <__visual-signals__/control.lua:205>"

[Zomis]

The erroring line is this:
https://github.com/Zomis/FactorioMods/blob/master/visual-signals_0.18.2/control.lua#L212
So basically the new player didn't have the GUI root window.

So it's an easy fix.