Follow-up from 4d2f800677
4d2f800677
Closes #6172
... they're already frowned upon in our source code style guide, this now enforces the rule harder.
When CURL_SOCKET_BAD is returned in the callback, it should be treated as an error (CURLE_COULDNT_CONNECT) if no other socket is subsequently created when trying to connect to a server. Bug: http://curl.haxx.se/mail/lib-2015-06/0047.html