/search endpoint "service unavailable" with collection filters, when there is no user specified

[danieleguido]

Bug reported by @theorm
The API should throw an appropriate error message, not a 500:

http://localhost:3030/search?filters[0][type]=collection&filters[0][q]=local-bulk-test&group_by=raw&limit=2&skip=0&filters[1][type]=hasTextContents