Fix bug 1109289

The only problem with this change is that if an event has a vidly_template but not a vidlysubmission things can go wrong but I don't know if such situation is possible
Having to do the SQL query is inevitable but it's excessive to have to turn it into and ORM object when all we ever need is the `hd` attribute of one item. 
We can fix that by instead doing:
```python
for vidly_submission in vidly_submissions.values('hd'):
    hd = vidly_submission['hd']
    break
```

It might be premature optimization but it is after all something that gets called on every event on every request.