DetachedSong: use std::chrono::duration for start_ms and end_ms

src/queue/PlaylistEdit.cxx

@@ -479,8 +479,8 @@ playlist::SetSongIdRange(PlayerControl &pc, unsigned id,
 	}
 
 	/* edit it */
-	song.SetStartMS(start_ms);
-	song.SetEndMS(end_ms);
+	song.SetStartTime(SongTime::FromMS(start_ms));
+	song.SetEndTime(SongTime::FromMS(end_ms));
 
 	/* announce the change to all interested subsystems */
 	UpdateQueuedSong(pc, nullptr);

src/queue/QueueSave.cxx

@@ -53,7 +53,7 @@ static void
 queue_save_song(BufferedOutputStream &os, int idx, const DetachedSong &song)
 {
 	if (song.IsInDatabase() &&
-	    song.GetStartMS() == 0 && song.GetEndMS() == 0)
+	    song.GetStartTime().IsZero() && song.GetEndTime().IsZero())
 		/* use the brief format (just the URI) for "full"
 		   database songs */
 		queue_save_database_song(os, idx, song);