Session.php: Fix - close running session only if it is not already closed.

extension/qfq/qfq/store/Session.php

@@ -45,7 +45,10 @@ class Session {
      * Free a lock on the current session
      */
     public static function close() {
-        session_write_close();
+
+        if (self::$sessionOpen) {
+            session_write_close();
+        }
         self::$sessionOpen = false;
 
     }