How to get offline method callback?

consider this example:

```
Meteor.call 'doSomething', (err, suc) =>
if err
console.log 'error!'
else
console.log 'succes!'
```

When online this works fine. But when offline, there's never a callback. How to get success from Ground for a method call?

The issue names Meteor.call and the doSomething callback but no source file or test. Start by tracing how GroundDB handles Meteor method calls while offline, then determine the expected callback behavior and add coverage showing what happens when the call completes offline.

Written by the indexing model from the issue text.