Fix retaining cycle caused by timer on SuperpoweredIOSAudioIO

[luizv]

Commit Description

• Fix implementation of the stopTimer to prevent retaining cycles
• Change stopTimer from a NSTimer to dispatch_source_t object

Comment

• On a personal project I notice that instances of SuperpoweredIOSAudioIO could never be deallocated because of a strong reference kept by NSTimer. Dealloc would never be called.

• I changed the implementation of the stopTimer (originally a NSTimer) to a be a dispatch_source_t object. This way no strong reference to self was kept.

• It was a simple fix, that maintains the same intended functionality (calling everySecond method every second while SuperpoweredIOSAudioIO exists), with the benefit of preventing this memory leak.

Virtually no impact on compatibility
Also this change doesn't impact on compatibility. dispatch_source_t is available on:
iOS 4.0+, macOS 10.6+, tvOS 9.0+, watchOS 2.0+

[reddotrapbeat]

Okay

[gaborszanto]

Thanks for discovering this issue. The next build will have a simple [self release] after the timer is created. I think it's more compact solution.