Fix XSS vulnerability in _mbox argument handling (#1490417)

Aleksander Machniak

2015-05-30 b782815dacda55eee6793249b5da1789256206fc

 program/include/rcmail.php

@@ -1822,7 +1822,7 @@
            }
            else {
                $error = 'servererrormsg';
                $args  = array('msg' => $err_str);
                $args  = array('msg' => rcube::Q($err_str));
            }
        }
        else if ($err_code < 0) {