remove unnecessary lock

src/network.c

@@ -313,9 +313,7 @@ void transfer_blocking(CURL *curl)
     transfer.transferring = 1;
     curl_easy_setopt(curl, CURLOPT_PRIVATE, &transfer);
 
-    pthread_mutex_lock(&transfer_lock);
     CURLMcode res = curl_multi_add_handle(curl_multi, curl);
-    pthread_mutex_unlock(&transfer_lock);
 
     if(res > 0) {
         fprintf(stderr, "blocking_multi_transfer(): %d, %s\n",