Uncaught exception in e3.cve.NVD.search_by_cpe_name()

When the number of queries to NVD has reached its limit, the `search_by_cpe_name()` method crashes on `r.json()`.
The request status should be checked.
As the number of requests to NVD is limited, it would be good to either implement a retry, either keep in mind the startpage, so that, on failure, the next call does not exhaust the number of API calls.