Retrieves the current master volume level.
If successful, the volume level is returned, else -1 is returned. Use BASS_ErrorGetCode to get the error code.
|BASS_ERROR_INIT|| BASS_Init has not been successfully called.
|BASS_ERROR_NOTAVAIL||There is no volume control when using the "no sound" device.
|BASS_ERROR_UNKNOWN||Some other mystery problem!
When using multiple devices, the current thread's device setting (as set with BASS_SetDevice) determines which device this function call applies to.