curl: Shared HSTS cache accessed without lock

This is finding F5 in Andrew's report https://github.com/curl/curl/blob/455bebc2c7/lib/hsts.cL160-L168 https://github.com/curl/curl/blob/455bebc2c7/lib/http.cL3571 https://github.com/curl/curl/blob/455bebc2c7/lib/url.cL1441 https://github.com/curl/curl/blob/455bebc2c7/lib/url.cL265...