Correctly retrieve the output layout on macOS < 10.12.
Correctly retrieve the output layout on macOS < 10.12.

The method kAudioUnitProperty_AudioChannelLayout used to retrieve the channel layout wasn't introduced until 10.12. So we use kAudioDevicePropertyPreferredChannelLayout instead should it fails.

Fixes #448

kinetiknz/cubeb,kinetiknz/cubeb,kinetiknz/cubeb