Fix adding up of total play back time

vrobbler/apps/scrobbles/models.py

@@ -648,9 +648,7 @@ class Scrobble(TimeStampedModel):
             ).last()
             self.long_play_seconds = self.playback_position_seconds
             if last_scrobble:
-                self.long_play_seconds = int(
-                    last_scrobble.playback_position_seconds
-                ) + int(self.playback_position_seconds)
+                self.long_play_seconds = last_scrobble.long_play_seconds + self.playback_position_seconds
 
             self.save(
                 update_fields=[