Fix displaying all headers when they contain malformed characters (#1488666)

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Fix displaying all headers when they contain malformed characters (#1488666)
 - Fix decoding of HTML messages with UTF-16 charset specified (#1488654)
 - Fix quota capability detection so it can be overwritten by a plugin (#1488655)
 - Added template object 'frame'

program/steps/mail/headers.inc

@@ -24,7 +24,8 @@ if ($uid = get_input_value('_uid', RCUBE_INPUT_POST))
     $source = $RCMAIL->storage->get_raw_headers($uid);
 
     if ($source !== false) {
-        $source = htmlspecialchars(trim($source));
+        $source = trim(rcube_charset::clean($source));
+        $source = htmlspecialchars($source);
         $source = preg_replace(
             array(
                 '/\n[\t\s]+/',