* SQLstore: Fix fetching and deleting an inexistent playlist
xorm's session.Get() does not return an error if the raw does not exist.
It returns a boolean instead.
The playlist `sqlstore.GetPlaylist()` used to check only the error and in case
of inexistent UID didn't return an error.
(cherry picked from commit 4ff0f006dd)
Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>