_raix_push_notifications stopped being processed

First of all - GREAT plugin. Thank you Raix and other contributors for making this plugin possible!! Your hard work has had a positive impact on my application.

I noticed push notifications weren't going through for my app and investigated. I saw that the `_raix_push_notifications` collection had stopped being processed. Push notifications were going in but not coming out.

Looking at the code, I see the following inside a `Meteor.setInterval` function:

```
// Set send fence
isSendingNotification = true;
// ....
// ....
isSendingNotification = false;
```

My question is, if an error occurred between true and false, would it disable the queue until service restart? I think it would as the fence flag off would not be triggered. Note that a service restart fixed my issue which is why I was thinking perhaps this is what happened.

My mongo server is on compose.io and I wonder if the inherent unreliability of networks makes this safe to use in hosted mongo scenarios.

Any thoughts?

Trace processing of the `_raix_push_notifications` collection from the `Meteor.setInterval` callback, focusing on the `isSendingNotification` flag and the error path between setting it true and false. Confirm whether a failure can leave the queue blocked, then document or test the expected recovery behavior; the issue does not name a file or test, so completion criteria need clarification.

Written by the indexing model from the issue text.