Worker collection undefined

Not sure how it happened....

But one of our naught instances seemed to just magically crash with the following exception:

```
.../node_modules/naught/lib/master.js:130
var hash = collection.hash;
^
TypeError: Cannot read property 'hash' of undefined
at removeWorker (.../node_modules/naught/lib/master.js:130:24)
at setWorkerStatus (.../node_modules/naught/lib/master.js:114:21)
at Worker.onMessage (.../node_modules/naught/lib/master.js:190:7)
at Worker.emit (events.js:117:20)
at ChildProcess.emit (events.js:98:17)
at handleMessage (child_process.js:322:10)
at Pipe.channel.onread (child_process.js:349:11)
```

It kinda seems like somehow the `dying` worker status collection got removed? Can't quite figure out how or why :-s

Not sure if anyone has any thoughts? :-s

(It's kinda bad because it crashed the whole naught process...)

I can't find anything that indicates what operation was happening at the time either unfortunately :-s