Disabled clients should trigger callbacks

Without this, boilerplate like...

```javascript
raven.patchGlobal(function(success, err) {
  console.error(err.stack);
  process.exit(1);
});
```

...won't fire when the underlying client is disabled (i.e. no `SENTRY_DSN`).  However, the `uncaughtException` handler will still be registered, effectively swallowing errors.

This patch causes the client to pretend to have logged the request, allowing `patchGlobal` to trigger custom callbacks as would happen if it were enabled.