MDL-60281 general: various strict corrections for PHP7.2

- count() can only be called on arrays or Countable, it can not be called on null
- recordset is neither so iterator_count() should be used
- instanceof or get_class() can not be applied to non-objects
- class methods must have the same arguments as methods in parent class

cache/disabledlib.php

@@ -125,9 +125,10 @@ class cache_disabled extends cache {
      * Checks if the cache has the requested key.
      *
      * @param int|string $key Unused.
+     * @param bool $tryloadifpossible Unused.
      * @return bool
      */
-    public function has($key) {
+    public function has($key, $tryloadifpossible = false) {
         return false;
     }