Curl_http_connect: detect HTTPS properly after CONNECT

libcurl failed to check the correct struct for HTTPS after CONNECT was
issued to the proxy, so it didn't do the TLS handshake and subsequently
failed the connection. A regression released in 7.21.5 (introduced
around commit 8831000b).

Bug: http://curl.haxx.se/mail/lib-2011-04/0134.html
Reported by: Josue Andrade Gomes