add missing translation for email_error_isemail

Patrick Anders

2014-12-17 a20782eb1d1e71e95cfa71e61e093a315e9abe3d

 interface/web/mail/lib/lang/en_mail_forward.lng

@@ -6,4 +6,5 @@
$wb["duplicate_mailbox_txt"] = 'There is already a mailbox with this email address';
$wb['domain_txt'] = 'Domain';
$wb["source_txt"] = 'Source Email';
$wb['email_error_isemail'] = 'Please enter a valid email address.';
?>