Changed to use a different util function which does not call the converter repeatedly in a loop

in order to workaround the converter problem (bug 138578),
bug 120728, r=ducarroz, sr=sspitzer.

mailnews/mime/src/mimedrft.cpp

@@ -1154,7 +1154,7 @@ mime_insert_forwarded_message_headers(char            **body,
     // convert body from mail charset to UTF-8
     char *utf8 = NULL;
     nsAutoString ucs2;
-    if (NS_SUCCEEDED(nsMsgI18NConvertToUnicode(nsCAutoString(mailcharset), nsCAutoString(*body), ucs2))) {
+    if (NS_SUCCEEDED(ConvertToUnicode(mailcharset, *body, ucs2))) {
       utf8 = ToNewUTF8String(ucs2);
       if (NULL != utf8) {
         PR_Free(*body);