Error when calling /intermediate/button multiple times

### Context:

The `/intermediate/button` API endpoint can be called several times and, in theory, the last call should get a valid answer after the user presses a button in the device. For example, After calling the `/backup` endpoint and then calling the `/intermediate/button` endpoint, it is possible to cancel the call to `/intermediate/button` and the call that same endpoint again for getting a response after the user presses a button in the device.

### Problem:

The previous example fails randomly, because after the user presses a button in the device the correct answer is not returned to the last call to `/intermediate/button`, but it can be sent to any of the previous calls to `/intermediate/button` (randomly selected).

### Example test:

I used the app Postman to call the `/backup` API endpoint, and, after that, the `/intermediate/button` endpoint (as should normally be done) After that, I cancelled the request to `/intermediate/button` and called that same endpoint again, I did that 8 times before pressing a button in the hw wallet. Fiddler showed this:


The image shows the first call to `/backup` and 8 calls to `/intermediate/button`. All the last 8 connections show a green arrow because the system is still waiting for a response from the daemon, although the connections were canceled in Postman. The same behavior happens when cancelling a request made with a web browser, and also when cancelling requests to a Skycoin node, so it appears to be normal a behavior.

After that, I pressed a button in the hw wallet and the last call to `/intermediate/button` got this response:

```
{
"error": {
"message": "closed device",
"code": 500
}
}
```

However, the interesting part is that Fiddler showed this:


The correct answer was received by the fifth call to `/intermediate/button` (in other tests the correct answer was received by other request, so the result appears to be random). The image shows the same icon for the first 7 calls because the response was ignored by the client (because the request was cancelled), but the fifth call has a status code 200.