社会主义加班人

Hi,sir. I found a little error about nullptr in https://github.com/DJm00n/hidapi/blob/device_notify/windows/hid.c#L1036  

I noticed, the plugged devices before my testing program startup also can be callback. I think, hotplug just processes the hot plug events, but not existed devices.

yes. registe callback like this will not receive existed devices: `hid_hotplug_register_callback(0, 0, HID_API_HOTPLUG_EVENT_DEVICE_ARRIVED| HID_API_HOTPLUG_EVENT_DEVICE_LEFT, 0/*HID_API_HOTPLUG_ENUMERATE*/, hotplug_callback, this, &hotplug_handle);`