CORE-14037
- Fix buggy retrieval of the current calling Irp->Tail.Overlay.Thread.
- The 4th argument (KernelRoutine) to the KeInitializeApc() is **NOT**
optional; however its 5th argument (RundownRoutine) is.
So use the mandatory routine for freeing the allocated APC instead.
We don't use the rundown routine yet.
- Check whether the ExAllocatePoolWithTag() call failed or not before
queueing the allocated APC.