Fix warnings about undefined 'metadata' variables in debug.log

[kimhornung]

When WP debug is enabled, a number of warnings about undefined variables appear in the debug.log file.
However, it might depend on how the course/training is defined in SCORM for these warnings to appear.

Steps to reproduce

1. Add the following lines to wp-config.php to enable WP debug

define('WP_DEBUG', true);
define('WP_DEBUG_DISPLAY', false);
define('WP_DEBUG_LOG', true);

2. Edit a page (and if you are using the Block Editor, add a Classic block)

3. Use the "Insert a SCORM Cloud training link" button and insert a SCORM Cloud embed code.

4. Publish the page

Result:
The following warnings appears in the /wp-content/debug.log file:

[08-Nov-2022 15:49:00 UTC] PHP Notice:  Undefined property: RusticiSoftware\Cloud\V2\Model\CourseSchema::$metadata in <webroot>/scormcloud/scormcloudcontenthandler.php on line 56
[08-Nov-2022 15:49:00 UTC] PHP Notice:  Undefined variable: metadata in <webroot>/scormcloud/scormcloudcontenthandler.php on line 62