Infer platforms for (manual) jobs that do not have it and fix exception on v2020 reports

Fix a couple exceptions from the recent work dealing with disambiguating results based on image_platform as part of !114 (merged)

It should fix the exceptions here:

• the v2022dev3.0 report that includes manual tests: https://lavaphabbridge.apertis.org/report/v2022dev3/20210915.0019/apt
• the most recent v2020 report that fails during rendering: https://lavaphabbridge.apertis.org/report/v2020/20211130.0/apt

Task: https://phabricator.apertis.org/T8372