Olivier Fourdan authored Nov 19, 2018 and Jonas Ådahl committed Nov 19, 2018

If a device (virtual or real) is removed while there are remaining
events queued for that device, the event loop may try to access the
event freed memory.

To avoid the issue, add a reference to the device when the event is
created or copied, and remove the reference once the device is freed.

Closes: #393