Wrong ISM decoder print-out

There is a bug in the ISM decoder printout in function preview_indices(): a wrong number of transported objects is print-out when the number of output channels is higher or equal to 4.

E.g. for 4ISM and FOA output, the printout is as follows:

Output sampling rate:   48000 Hz
Bitrate:                256.00 kbps
Input configuration:    ISM: 1 transport channel(s)
Output configuration:   Ambisonics: First Order (FOA)

while the correct one is

Output sampling rate:   48000 Hz
Bitrate:                256.00 kbps
Input configuration:    ISM: 4 transport channel(s)
Output configuration:   Ambisonics: First Order (FOA)