Set User-Agent: header field in HTTP request for curl downloads

Some servers (for example wikimedia.org) don't allow downloads
with the default user agent of libcurl and send HTTP status 403,
so OCR for images on such servers fails.

Setting the user agent to "Tesseract OCR" allows OCR for images
on those servers.

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/api/baseapi.cpp

@@ -1184,6 +1184,10 @@ bool TessBaseAPI::ProcessPagesInternal(const char *filename, const char *retry_c
       if (curlcode != CURLE_OK) {
         return error("curl_easy_setopt");
       }
+      curlcode = curl_easy_setopt(curl, CURLOPT_USERAGENT, "Tesseract OCR");
+      if (curlcode != CURLE_OK) {
+        return error("curl_easy_setopt");
+      }
       curlcode = curl_easy_perform(curl);
       if (curlcode != CURLE_OK) {
         return error("curl_easy_perform");