Chech for mb_convert_encoding first because mbstring is optional for RoundCube + add some phpdoc

program/lib/washtml.php

@@ -187,7 +187,8 @@ class washtml
     //Charset seems to be ignored (probably if defined in the HTML document)
     $node = new DOMDocument('1.0', $config['charset']);
     $full = true;
-    $html = mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8');
+    if (function_exists('mb_convert_encoding'))
+      $html = mb_convert_encoding($html, 'HTML-ENTITIES', $config['charset']);
     @$node->loadHTML($html);
     return self::dumpHtml($node, $config, $full);
   }

program/steps/mail/func.inc

@@ -514,9 +514,15 @@ function rcmail_get_messagecount_text($count=NULL, $page=NULL)
 
 
 /**
+ * Convert the given message part to proper HTML
+ * which can be displayed the message view
  *
+ * @param object rcube_message_part Message part
+ * @param bool  True if external objects (ie. images ) are allowed
+ * @param bool  True if part should be converted to plaintext
+ * @return string Formatted HTML string
  */
-function rcmail_print_body($part, $safe=FALSE, $plain=FALSE)
+function rcmail_print_body($part, $safe=false, $plain=false)
 {
   global $REMOTE_OBJECTS;