This fixes a memory leak when CURLOPT_LOGIN_OPTIONS is used, together with
connection reuse.
I found this with oss-fuzz on GDAL and curl master:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9582
I couldn't reproduce with the oss-fuzz original test case, but looking
at curl source code pointed to this well reproducable leak.
Closes #2790
Curl_safefree(old_conn->user);
Curl_safefree(old_conn->passwd);
+ Curl_safefree(old_conn->options);
Curl_safefree(old_conn->http_proxy.user);
Curl_safefree(old_conn->socks_proxy.user);
Curl_safefree(old_conn->http_proxy.passwd);