fix - HTTPClient connection keep-alive duplicate Headers #4208

(cherry picked from commit 6ad226ac38)

core/io/http_client.cpp

@@ -301,6 +301,7 @@ Error HTTPClient::poll(){
 					chunked=false;
 					body_left=0;
 					chunk_left=0;
+					response_str.clear();
 					response_headers.clear();
 					response_num = RESPONSE_OK;