If any requests come back connection refused, skip over them.

Note 'out' is initialised as 'YKCLIENT_OK', so it is vital
to set it to something else before continuing

Perhaps I should have used a different/new return code?
msg->data.result can be lots of other things too. http://curl.haxx.se/libcurl/c/libcurl-errors.html

I've only caught CURLE_OK and two error conditions specifically.

This addresses https://github.com/Yubico/yubico-c-client/issues/25