deleting a track while it's being scanned causes a phantom entry in the library

Steps to reproduce:
1. import a song
2. while the song is scanning, delete it from the library.
3. wait for the song to be done scanning.

now the song will show up again in your library, but you can't play it. Trying to play it results in this error on the server console:

```
Error opening FILE_NAME_HERE.mp3 Error: open file failed
at Error (native)
```

The file is actually gone. All that remains is a ghost in the library metadata.