When returning sound, a mono sound should be returned as a (mono) sound object and stereo sounds as an array of two sound objects. (More than 2 channels are not currently supported).

If Nyquist returns a mono sound as an array, it should throw an appropriate error:
"Nyquist returned one audio channel as an array.\n"

As of https://github.com/audacity/audacity/commit/67cec5ad8
Audacity incorrectly returns the error message:
"Nyquist returned too many audio channels.\n"

The error message as now is confusing and incorrect (only one channel is returned, which is not "too many").

This bug is due to incorrectly declaring mCurNumChannels as unsigned. It needs to be a signed integer because nyx_get_audio_num_channels may return a negative value. (It also causes multiple compiler warnings).

Assigned to myself.