MDL-76041 mod_bigbluebuttonbn: Exception on Recording only page

* This fixes a the parameter provided to the get_recordings method of recording class

mod/bigbluebuttonbn/classes/external/get_recordings.php

@@ -113,7 +113,7 @@ class get_recordings extends external_api {
                 if ($groupid) {
                     $instance->set_group_id($groupid);
                 }
-                $recordings = $instance->get_recordings([], $instance->get_instance_var('recordings_deleted'));
+                $recordings = $instance->get_recordings([], $instance->get_instance_var('recordings_deleted') ?? false);
                 $tabledata = recording_data::get_recording_table($recordings, $tools, $instance);
 
                 $returnval['tabledata'] = $tabledata;

mod/bigbluebuttonbn/classes/instance.php

@@ -406,7 +406,7 @@ EOF;
      * Helper to get an instance var.
      *
      * @param string $name
-     * @return string
+     * @return mixed|null
      */
     public function get_instance_var(string $name) {
         $instance = $this->get_instance_data();
@@ -1105,7 +1105,7 @@ EOF;
      * @param bool $viewdeleted view deleted recordings ?
      * @return recording[]
      */
-    public function get_recordings(array $excludedid = [], $viewdeleted = false): array {
+    public function get_recordings(array $excludedid = [], bool $viewdeleted = false): array {
         // Fetch the list of recordings depending on the status of the instance.
         // show room is enabled for TYPE_ALL and TYPE_ROOM_ONLY.
         if ($this->is_feature_enabled('showroom')) {