i3companion xkeybinder: Ignore unbound KeyPress events
i3companion xkeybinder: Ignore unbound KeyPress events

We can get KeyPress events we haven't explicitly asked for in some
circumstances, so just ignore any we don't recognise.

e.g. If we have grabbed Win+c and the user holds Win, presses c, then
presses Shift without releasing Win will cause us to receive a KeyPress
for Win+Shift.

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