Make Input Handling Code More Robust To Malfunctioning Devices

[bluebandit21]

From a recently resolved issue in the developer Discord (see: here), unplayable lag was caused by a USB device with intermittent connection being plugged into the computer while Etterna was running.

Ideally, our code should be more robust against this kind of issue -- a malfunctioning webcam shouldn't make Etterna unplayable.

Perhaps a fix would be to only check for new devices while not in gameplay?
I can't imagine anyone intentionally plugging a keyboard in halfway through a song and expecting it to immediately work.