Android: Avoid empty file format on the AudioRecorder app

On Android, we need to choose the first file format instead of the default file format.

Steps to reproduce:
1. Run AudioRecorder example on Android device
2. Leave File Container as Default file format
3. Click Output button for open  FileDialog

Actual:
  Initial file name is "output."
  File format missing.

Expected:
 Initial file name should be as eg. "output.aac"