abcde should not write over "unknown" folder

[Reuben Firmin]

Binary package hint: abcde

When abcde cannot identify the artist / album, the default name assigned to the output folder is "Unknown_Artist-Unknown_Album".

If abcde is being called from a script to rip many CDs at once, every time a CD cannot be identified, the Unknown_Artist-Unknown_Album folder is overwritten. It _does_ make sense to overwrite identified albums (perhaps the user is re-ripping with a different codec, or similar), but given that many albums may be "unknown", abcde should have a special case that takes care of this logic.

I suggest that the folders be named sequentially, e.g. Unknown_Artist-Unknown_Album_1, Unknown_Artist-Unknown_Album_2, etc.

Thanks