Fixed a bug that prevented the display of multiple empty playlists

Turned out this bug was already fixed two years ago but unfortunately
it made its way back again. It was solved in #9642 but back then another
method was used for querying playlists from db (for add playlist dialog) then in
ef4a623 was introduced another method
which had the same problem as fixed in #9642 and which eventually replaced
original method in code for querying playlists from db (for add playlist dialog)

Author: dustdfg

app/src/main/java/org/schabi/newpipe/database/playlist/dao/PlaylistStreamDAO.kt

@@ -118,7 +118,7 @@ interface PlaylistStreamDAO : BasicDAO<PlaylistStreamEntity> {
         LEFT JOIN streams
         ON streams.uid = stream_id AND :streamUrl = :streamUrl
 
-        GROUP BY playlist_id
+        GROUP BY playlists.uid
         ORDER BY display_index, name
         """
     )