Notifies that a transfer request is cancelled. It will be flushed by the streaming device when completed. Cancellation is normal and happens regularly; for example, whenever a sound stops before the end or stops looping. It happens even more frequently when buffering (AkDeviceSettings::fTargetAutoStmBufferLength and AkDeviceSettings::uGranularity) is large and when you low-level IO hook accepts many concurrent requests at the same time.
Referenced by BatchCancel().