ZP-864 Do not convert if charset encoding is already UTF-8.

Released under the Affero GNU General Public License (AGPL) version 3.

src/lib/request/request.php

@@ -256,7 +256,7 @@ class Request {
                     ZLog::Write(LOGLEVEL_ERROR, "Request->ProcessHeaders(): mb_detect_encoding failed to detect the Authorization header charset. It's possible that user won't be able to login.");
                 }
             }
-            if ($encoding) {
+            if ($encoding && stripos($encoding, "utf-8") === false) {
                 ZLog::Write(LOGLEVEL_DEBUG, sprintf("Request->ProcessHeaders(): mb_detect_encoding detected '%s' charset. Authorization header will be converted to UTF-8 from it.", $encoding));
                 self::$authUser = mb_convert_encoding(self::$authUser, "UTF-8", $encoding);
                 self::$authPassword = mb_convert_encoding(self::$authPassword, "UTF-8", $encoding);