Throw not found exception when photo item doesn't exist in prepare_photo_data()
Throw not found exception when photo item doesn't exist in prepare_photo_data()

- Addresses part of https://github.com/friendica/friendica/issues/8000#issuecomment-573883153

annando/friendica,fabrixxm/friendica,annando/friendica,fabrixxm/friendica,friendica/friendica,friendica/friendica,annando/friendica,annando/friendica,friendica/friendica,friendica/friendica,fabrixxm/friendica,tobiasd/friendica,tobiasd/friendica,friendica/friendica,tobiasd/friendica,tobiasd/friendica,fabrixxm/friendica,tobiasd/friendica,annando/friendica,fabrixxm/friendica