comment out empty language string

The empty string is not translatable in the translation interface and
causes all languages to be <100%

This is an alternative approach to #2164

inc/lang/en/lang.php

@@ -370,5 +370,5 @@ $lang['page_nonexist_rev']     = 'Page did not exist at %s. It was subsequently
 $lang['unable_to_parse_date']  = 'Unable to parse at parameter "%s".';
 $lang['email_signature_text'] = 'This mail was generated by DokuWiki at
 @DOKUWIKIURL@';
-$lang['email_signature_html'] = '';
-//Setup VIM: ex: et ts=2 :
+#$lang['email_signature_html'] = ''; # the empty default will copy the text signature, you can override it in a local lang file
+