[native] Fix missing media mission report steps

Summary: Some media mission steps were missing when encryption failed. It turns out that they weren't appended in the failure callback function. Added inline comments to explain the places.

Test Plan: Triggered encryption failure (write_file_failed) and confirmed that the steps were appended in the correct order.

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8737