load_channels_as_audio fails when file has 1 channel

[sammlapp]

Librosa returns a 1d array of samples instead of a 2d array with load(...mono=False) if the file only has one channel. This causes load_channels_as_audio to raise a ValueError when it tries to make one Audio object per [first dimension of sample array]. The fix is easy - just make a single object if the sample array is 1D. The function should still return a list of Audio object(s) for consistency.