fix(podcast-activity): check if transcript and chapters are set before including them in audio

                'type' => 'Link',

                'mediaType' => $episode->audio->file_mimetype,

            ],

            'transcript' => $episode->transcript->file_url,

            'chapters' => $episode->chapters->file_url,

        ];

        if ($episode->transcript !== null) {

            $this->audio['transcript'] = $episode->transcript->file_url;

        }

        if ($episode->chapters !== null) {

            $this->audio['chapters'] = $episode->chapters->file_url;

        }

        $this->comments = url_to('episode-comments', $episode->podcast->handle, $episode->slug);

        if ($episode->published_at !== null) {