Check the playing status of a specific channel.
int Mix_Playing(int channel);
Returns non-zero if channel is playing, zero otherwise. If
channel is -1, return the total number of channel playings.
If the channel is currently playing, this function returns 1. Otherwise it returns 0.
If the specified channel is -1, all channels are checked, and this function returns the number of channels currently playing.
You may not specify MAX_CHANNEL_POST for a channel.
Paused channels are treated as playing, even though they are not currently making forward progress in mixing.
This function is available since SDL_mixer 2.0.0.