IntegrityError at /api/v1/quotes/2673/vote - duplicate key value violates unique constraint "lecturers_quotevote_user_id_3ecc6f4b83d4492b_uniq"

```
IntegrityError at /api/v1/quotes/2673/vote
duplicate key value violates unique constraint "lecturers_quotevote_user_id_3ecc6f4b83d4492b_uniq"
DETAIL:  Key (user_id, quote_id)=(3620, 2673) already exists.
```

sollte ähnlich wie #491 eigentlich schon abgefangen sein...