Mouse example crashes when using keyboard and mouse

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In the example examples/mouse/mouse.go I get the following error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x49fa4a]

goroutine 1 [running]:
main.main()
        /home/abshield/go/src/github.com/gbin/goncurses/examples/mouse/mouse.go:89 +0x64a
exit status 2

Source is unmodified, up to date with master branch.

To reproduce: Run mouse.go (using go run or go install). Select a choice using the mouse (it doesn't matter which one) and then use the arrow keys to try and change the choice. Program crashes.

Using Ubuntu 19.04 Disco, tested over ssh+tmux and also locally.

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Seems to be a duplicate of https://github.com/rthornton128/goncurses/issues/29