Limit /redir links to private posts

- This allows to share public post links with anonymous users

include/conversation.php

@@ -177,7 +177,7 @@ function localize_item(&$item)
 
 	// add sparkle links to appropriate permalinks
 	// Only create a redirection to a magic link when logged in
-	if (!empty($item['plink']) && Session::isAuthenticated()) {
+	if (!empty($item['plink']) && Session::isAuthenticated() && $item['private'] == Item::PRIVATE) {
 		$author = ['uid' => 0, 'id' => $item['author-id'],
 			'network' => $item['author-network'], 'url' => $item['author-link']];
 		$item['plink'] = Contact::magicLinkByContact($author, $item['plink']);