Fixed a problem with curl_pair specialization.
Fixed a problem with curl_pair specialization.

susnux/curlcpp,capturePointer/curlcpp,ellivr/curlcpp,ellivr/curlcpp,JosephP91/curlcpp,guker/curlcpp,capturePointer/curlcpp,susnux/curlcpp,JosephP91/curlcpp,gaomingyang21/curlcpp,guker/curlcpp,gaomingyang21/curlcpp