http: Fix NULL vpninfo->hostname pointer on redirect

Commit 1fe3f43 (Make openconnect_set_hostname() clear
vpninfo->peer_addr, use it more often) broke NEWHOST redirects:

    $ ./openconnect -v vpn.ufl.edu
    POST https://vpn.ufl.edu/
    Attempting to connect to server 128.227.166.118:443
    SSL negotiation with vpn.ufl.edu
    Matched DNS altname 'vpn.ufl.edu'
    Connected to HTTPS on vpn.ufl.edu
    Got HTTP response: HTTP/1.0 302 Temporary moved
    Content-Length: 0
    Cache-Control: no-cache
    Pragma: no-cache
    Connection: Close
    Date: Tue, 31 Dec 2013 19:43:47 GMT
    Location: https://ctx36-vpn-asa5500-1-g10-1.ns.ufl.edu/
    HTTP body length:  (0)
    POST https://(null)/
    Segmentation fault

Fix this by populating vpninfo->hostname with the correct value.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>

http.c

@@ -759,7 +759,7 @@ static int handle_redirect(struct openconnect_info *vpninfo)
 		}
 
 		if (strcasecmp(vpninfo->hostname, host) || port != vpninfo->port) {
-			openconnect_set_hostname(vpninfo, NULL);
+			openconnect_set_hostname(vpninfo, host);
 			vpninfo->port = port;
 
 			/* Kill the existing connection, and a new one will happen */