Allow decoding files with empty multichannel signal groups #96
Description
During testing customer streams we've discovered several files that could not be decoded. The reason turned out to be Ittiam decoder rejecting MCTConfig without any channels – and those files have two configurations, first one encompassing all channels and the second one having none. Since the second configuration is not used, the files can be decoded if such configuration existence is tolerated.
P.S. In case when such empty configuration is used, the decoder will error out on zero channel count as inadvertently discovered in the earlier reported issue #94.