Skipping empty categories in restore. They shouldn't exist but

I've received some examples of this these days.

Merged from MOODLE_14_STABLE

backup/restorelib.php

@@ -990,6 +990,8 @@
             if ($info !== true) {
                 //Iterate over each category
                 foreach ($info as $category) {
+                    //Skip empty categories (some backups can contain them)
+                    if (!empty($category->id)) {
                         $catrestore = "quiz_restore_question_categories";
                         if (function_exists($catrestore)) {
                             //print_object ($category);                                                //Debug
@@ -1000,6 +1002,7 @@
                         }
                     }
                 }
+            }
         } else {
             $status = false;
         }