Side-effect on request() when registering multiple input-events

Nobody has claimed this yet.

I experience a side-effect on request() when registering multiple input-events. See the following code:

```
const InputEvent = require('input-event');
const request = require('request');

// Register the callback functions
const input0 = new InputEvent('/dev/input/event0');
const keyboard0 = new InputEvent.Keyboard(input0);

const input1 = new InputEvent('/dev/input/event1');
const keyboard1 = new InputEvent.Keyboard(input1);

console.log('start request()');
request.get('http://google.com', () => {
console.log('received result');
});
```

this leads to `start request()`, but then it hangs and `received result` is not reached.

if the `input1`/`keyboard1` lines are commented out, the `request()` call works as expected.

why does input-event have such side-effects? and how to avoid this?

Start by running the minimal reproduction from the issue with one and then two /dev/input/event devices, comparing the request.get callback behavior. Trace the input-event and request entry points involved in registering the two Keyboard instances, and consider the issue resolved when the cause of the hang and a verified fix or avoidance path are identified.

Written by the indexing model from the issue text.