Add authentication failure callback

[Jerry0022]

Thanks for your great API. It works perfectly!
But! If I set a wrong API key or no API key there is an exception thrown in the http thread...
Exception in thread "Downstream Thread"
java.lang.NullPointerException
com.darkprograms.speech.recognizer.GSpeechDuplex$1.run(GSpeechDuplex.java:197)

Can you enable a possibility to catch it via callback for example?

[Skylion007]

Hmm, I see. I really do need to fix that. When I wrote that class, I knew next to nothing about multithreading. That is definitely on my long list of things to do.

There is even an if statement that I added awaiting an implementation of that feature. If you are willing to add the callback, I will gladly merge it in.

[Jerry0022]

Please see pull request ;)

[Skylion007]

@Jerry0022 Protip; In the future please reference the issue number instead as it will provide an hyperlink to the pull request like so: #64