progress callback: skip last callback update on errors

When an error has been detected, skip the final forced call to the
progress callback by making sure to pass the current return code
variable in the Curl_done() call in the CURLM_STATE_DONE state.

This avoids the "extra" callback that could occur even if you returned
error from the progress callback.

Bug: http://curl.haxx.se/mail/lib-2014-06/0062.html
Reported by: Jonathan Cardoso Machado