enumerate_hotplug can yield devices twice #23
Description
If a device is plugged in immediately when enumeration is started (after it already connected to the HotplugMonitor), the device will be yielded by the read_dir enumeration, and then again due to the hotplug event.
This is not good, since it can lead to applications misbehaving when they process events from two instances of the same device. Luckily, it is also fairly rare, so might not be a problem in practice. If it does happen, a workaround is to simply unplug the device and plug it back in.
It isn't immediately obvious how a proper fix for this would look like. We cannot open the HotplugMonitor after we've already yielded all the read_dir devices, since that might miss some (which is worse than yielding a device twice).