I think that this switch statement also needs to handle case 0, otherwise you see a bunch of internal errors for normal processing arrangements. They show up in the application test suite quite a bit, for example:

  Process MIDI with vstxsynth plugin: INTERNAL ERROR: Cannot handle more than 8 speaker channels
  This should not have happened. Please take a minute to report a bug.
  Support website: https://github.com/teragonaudio/mrswatson/issues
  Support email: support@teragonaudio.com
INTERNAL ERROR: Cannot handle more than 8 speaker channels
  This should not have happened. Please take a minute to report a bug.
  Support website: https://github.com/teragonaudio/mrswatson/issues
  Support email: support@teragonaudio.com
OK
  Process effect chain: INTERNAL ERROR: Cannot handle more than 8 speaker channels
  This should not have happened. Please take a minute to report a bug.
  Support website: https://github.com/teragonaudio/mrswatson/issues
  Support email: support@teragonaudio.com