The incremental scan's orphan cleanup and RemoveFromLibrary deleted
audio_files rows without first filling the playlist phantom columns, so
a track removed from the library folder outside YellowJacket (or
removed from the library) became a permanently empty playlist row that
nothing could re-link — the same bug #183 fixed on the full-rescan and
retire paths, on the two paths it missed.
Add a scoped PreservePlaylistPhantomsForFiles and run it in the same
transaction as the deletes on both paths.
Closes#246
