Don't render a quote link if discussion is closed

Author: atelomycterus

vanilla/plugins/Quotes/class.quotes.plugin.php

@@ -264,6 +264,11 @@ protected function addQuoteButton($sender, $args) {
             return;
         }
 
+        $isClosed = ((int)$discussion->Closed) == 1;
+        if ($isClosed) {
+            return;
+        }
+
         if (!Gdn::session()->UserID) {
             return;
         }