find_track_root() now issues a log message if it finds a track outside

find_track_root() now issues a log message if it finds a track outside
any collection.  Should make it clearer what's going on if something
believes the answer and crashes.

track_to_words() now includes a bodge for such tracks to avoid a
crash.  Ultimately the answer is to expunge such tracks from the
database but while my db is in a bizarre state it's worth making the
code a bit more robust.