Request to /collection/<missing>/items returns 200

[duckontheweb]

Ported from stac-utils/stac-fastapi#120.

Original Issue:

If I make a request to an endpoint for a collection that doesn't exists, I get a 404

In [14]: import requests

In [19]: r = requests.get("https://pct-pqe-staging.westeurope.cloudapp.azure.com/stac/v1/collections/not-a-collection")

In [20]: r.status_code
Out[20]: 404

But if I make a request to that collection's /items I get a 200, and the response includes an empty FeatureCollection.

In [21]: r = requests.get("https://pct-pqe-staging.westeurope.cloudapp.azure.com/stac/v1/collections/not-a-collection/items")

In [22]: r.status_code
Out[22]: 200

In [23]: r.json()
Out[23]:
{'type': 'FeatureCollection',
 'features': [],
 'links': [],
 'context': {'returned': 0, 'matched': 0}}

I wanted to verify that this is the expected behavior. I didn't find anything in the API spec, but I admittedly didn't look too closely.

Reported in TomAugspurger/stac-dask-discussion#1