Cannot unregister unregistered terrific component

[janbiasi]

I'm submitting a ...

[ ] Regression (behavior that used to work and stopped working in a new release)
[x] Bug report 
[ ] Feature request
[ ] Documentation issue or request

Current behavior

Expected behavior

It should not try unregister an unregistered component - or at least not throw an error. Beside that, the error should also show in which process the failure happened (e.g. unregisterComponent(...)).

Minimal reproduction of the problem with instructions

Call TerrificBridge.unregisterComponent(...) in the components componentWillUnmount hook without registering it in the componentDidMount hook.

What is the motivation / use case for changing the behavior?

Better debugging and preventing fatal errors.

Please tell us about your environment

TerrificBridge version: 1.2.5


Browser:
- [x] Every Browser
- [ ] Chrome (desktop) version XX
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ ] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version XX
- [ ] Edge version XX
 
For Tooling issues:
- Node version: 6.2 
- Platform: Mac 

Others: