CID 1508987: Unchecked return value from library

[maskit]

328      if (curl) {
     	CID 1508987 (#1 of 3): Unchecked return value from library (CHECKED_RETURN) [[select issue](https://scan6.scan.coverity.com/defectInstanceId=34730123&fileInstanceId=162214413&mergedDefectId=1508987)]
329        curl_easy_setopt(curl, CURLOPT_URL, _url.c_str());
   	
CID 1508987 (#3 of 3): Unchecked return value from library (CHECKED_RETURN)
3. check_return: Calling curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data) without checking return value. This library function may fail and return an error code.
330        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
     	CID 1508987 (#2 of 3): Unchecked return value from library (CHECKED_RETURN) [[select issue](https://scan6.scan.coverity.com/defectInstanceId=34730164&fileInstanceId=162214413&mergedDefectId=1508987)]
331        curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, curl_error);
332