url.c: fix endless loop upon transport connection timeout

Jerry Wu detected and provided detailed info about this issue.

lib/url.c

@@ -5119,6 +5119,12 @@ CURLcode Curl_setup_conn(struct connectdata *conn,
 
       result = ConnectPlease(data, conn, &connected);
 
+      if(result && !conn->ip_addr) {
+        /* transport connection failure not related with authentication */
+        conn->bits.tcpconnect[FIRSTSOCKET] = FALSE;
+        return result;
+      }
+
       if(connected) {
         result = Curl_protocol_connect(conn, protocol_done);
         if(CURLE_OK == result)