Crash in QThreadPool::clear()

There is a crash in QThreadPool::clear()  when auto-deleting QRunnables are being used. 

Attachment a very simple example project which does this in a loop:

1. Calls QThreadPool::clear()
2. Starts a bunch of runnables (~500) in QThreadPool. QRunnable::autoDelete() = true
3. goto 1

After a few iterations it crashes on QThreadPool::clear(). This happens consistently

I think the culprit is this commit. I've tried reverting it and the crash disappears.