Set res=NULL after calling freeaddrinfo().

Fixes crash on OS X (and double-free everywhere else) after a getaddrinfo()
succeeds, but the connect fails after returning EWOULDBLOCK/EAGAIN/etc.

Reported by Michael Montague (thanks!)

src/syncterm/conn.c

@@ -494,6 +494,7 @@ int conn_socket_connect(struct bbslist *bbs)
 
 connected:
 	freeaddrinfo(res);
+	res=NULL;
 	nonblock=0;
 	ioctlsocket(sock, FIONBIO, &nonblock);
 	if(!socket_check(sock, NULL, NULL, 0)) {