fix washing of HTML encoded in something other than UTF-8

CHANGELOG

@@ -5,6 +5,7 @@ CHANGELOG RoundCube Webmail
 - Speedup UI by using sprites for (toolbar) buttons
 - Fix charset names with X- prefix handling
 - Fix displaying of HTML messages with unknown/malformed tags (#1486003)
+- Fix HTML washing of non-UTF8 messages
 
 RELEASE 0.3-RC1
 ---------------

program/lib/washtml.php

@@ -246,6 +246,7 @@ class washtml
     //Charset seems to be ignored (probably if defined in the HTML document)
     $node = new DOMDocument('1.0', $this->config['charset']);
     $this->extlinks = false;
+    $html = mb_convert_encoding($html, 'HTML-ENTITIES', $this->config['charset']);
     @$node->loadHTML($html);
     return $this->dumpHtml($node);
   }