collection context for legacy redirect

I just checked legacy for the url and I got http://cnx.org/content/m16026/latest/?collection=col10522/latest

So it should be `collection` not `collection_context`?  Or are there some urls that use `collection_context`?

I think it would be better to change this line to
```python
    if params.get('collection'):
```
So if collection is empty (i.e. `?collection=`) the condition won't evaluate to true