tool_operate: Fix showing HTTPS-Proxy options on CURLE_SSL_CACERT

- Show the HTTPS-proxy options on CURLE_SSL_CACERT if libcurl was built
  with HTTPS-proxy support.

Prior to this change those options were shown only if an HTTPS-proxy was
specified by --proxy, but that did not take into account environment
variables such as http_proxy, https_proxy, etc. Follow-up to e1187c42.

Bug: https://github.com/curl/curl/issues/1331
Reported-by: Nehal J Wani