[Android] Handle errors better

[shubhamsinghmutualmobile]

I see the following crashes in my app's crashlytics window (on Android only):

1. 
2. 

But since I have wrapped my startDfu() method call inside a try-catch block, I expected this error to be handled and not crash the app. This would've been true if the startDfu future caught the error in the first place, but it seemingly does not.

Ideally, this error should be passed by the library to its own onError callback.

[shubhamsinghmutualmobile]

@juliansteenbakker Could you please help with this?