Fix filenames charset handling (#1488946)

plugins/zipdownload/zipdownload.php

@@ -30,9 +30,9 @@ class zipdownload extends rcube_plugin
 		}
 
 		$rcmail = rcmail::get_instance();
-		$this->charset = $rcmail->config->get('zipdownload_charset', RCUBE_CHARSET);
 
 		$this->load_config();
+		$this->charset = $rcmail->config->get('zipdownload_charset', RCUBE_CHARSET);
 		$this->add_texts('localization');
 
 		if ($rcmail->config->get('zipdownload_attachments', 1) > -1 && ($rcmail->action == 'show' || $rcmail->action == 'preview'))
@@ -265,8 +265,8 @@ class zipdownload extends rcube_plugin
 	 */
 	private function _convert_filename($str, $from = RCUBE_CHARSET)
 	{
-		return strtr(rcube_charset::convert($str, $from, $this->charset), array(':'=>'', '/'=>'-'));
+        $str = rcube_charset::convert($str, $from == '' ? RCUBE_CHARSET : $from, $this->charset);
+
+		return strtr($str, array(':'=>'', '/'=>'-'));
 	}
 }
-
-?>