devmgmt_new: HTREE\ROOT\0 is shown as "Unknown device" in Device Manager

Device Manager shows an "Unknown device" under "Other Devices".

Properties say its Device Instance ID is HTREE\ROOT\0, i.e. the hardware enumeration root.

This was fixed in devmgmt before (in r57316), but it's showing up again, so this is a regression.
Guilty revision is r69546 (thanks thc)