FIX behavior on /sp.search?q=ecog on default restype

- Currently the `get_search()` method only deals with `json` types and raises 400 on others.
- However, since the search form is targeted to `GET /sp.search`, it could even happen on browser when javascript is not enabled.
- 4 lines of codes added to deal with the default case.


I'm not sure about what the `opensearch` resformat does, so feel free to correct it if needed.