net: CurlHttpClient: Call curl_easy_reset() to fix error 'rewinding of the data'

@okman334 reported an error when using the curl HTTP client after commit
775291f ("net: Allow curl handle in CurlHttpClient to be kept alive"):

   error: curl error: Send failed since rewinding of the data stream failed.

Fix this by calling `curl_easy_reset()` before setting curl options. It
reinitializes all options previously set on a specified curl handle to
the default values while keeping the connection alive.

Closes: #340
Reported-by: @okman334
Fixes: 775291f ("net: Allow curl handle in CurlHttpClient to be kept alive")
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>

Author: ammarfaizi2

src/net/CurlHttpClient.cpp

@@ -45,6 +45,7 @@ static std::size_t curlWriteString(char* ptr, std::size_t size, std::size_t nmem
 std::string CurlHttpClient::makeRequest(const Url& url, const std::vector<HttpReqArg>& args) const {
     CURL* curl = getCurlHandle(this);
 
+    curl_easy_reset(curl);
     std::string u = url.protocol + "://" + url.host + url.path;
     if (args.empty()) {
         u += "?" + url.query;