use unique name as path

[jcyuan]

the devicePath usually does not work for virtual devices, the path will be empty, this new way will work for both physics audio/video devices and virtual devices btw, FFmpeg uses this way to get the unique path too.

[derrod]

Seems to work fine for me, and does produce a result for devices where it was previously empty.

However from the OBS perspective we'd probably need to figure out a migration path.