Found another place where deleted user needs to be checked.

Continuation from earlier PR for handling null users.
/cc @zendesk/samson @grosser 

### References

### Risks
 - None
This block can be simplified to
```
user.try(:name) || 'Deleted User'
```

with a new cached method:

```
def user
  return @user if defined?(@user)
  @user = User.with_deleted { User.where(id: id).first }
end