Revert broken part of cd66852f

"create appendCopy method in OUStringBuffer"; response_body is a std::string

Change-Id: I58ab982c87fa568fdac8e3c72fbcb0e071d73228

desktop/source/app/updater.cxx

@@ -571,7 +571,7 @@ std::string download_content(const OString& rURL, bool bFile, OUString& rHash)
     {
         OUString aTempFileURL = aTempFile.GetURL();
         OString aTempFileURLOString = OUStringToOString(aTempFileURL, RTL_TEXTENCODING_UTF8);
-        response_body.append(aTempFileURLOString);
+        response_body.append(aTempFileURLOString.getStr(), aTempFileURLOString.getLength());
 
         aTempFile.EnableKillingFile(false);