bugfix: no sql error when adding ticket via ebok and there is no default category set for userpanel

Author: interduo

lib/LMSManagers/LMSHelpdeskManager.php

@@ -1255,8 +1255,10 @@ public function TicketAdd($ticket, $files = null)
 
         if (!empty($ticket['categories'])) {
             foreach (array_keys($ticket['categories']) as $catid) {
-                $this->db->Execute('INSERT INTO rtticketcategories (ticketid, categoryid)
-					VALUES (?, ?)', array($id, $catid));
+                if (!empty($catid)) {
+                    $this->db->Execute('INSERT INTO rtticketcategories (ticketid, categoryid)
+						VALUES (?, ?)', array($id, $catid));
+                }
             }
         }