Number of playing sound channels; also indicated in the 'count' column
of the Statistics Panel.
This number is increased when a sound starts to play through a snd_play or ent_playsound function; it is decreased when the sound stops.
0 .. 32
(dependent on the sound hardware)
PANEL* sounds_indicator =
digits(0, 0, 5, *, 1, num_sounds); // show number of playing sound channels
flags = SHOW;