Fix message and error for artifact history view bug

This error happened when I clicked on history when browsing an origin: TypeError: 'NoneType' object is not subscriptable https://archive.softwareheritage.org/browse/origin/https://hal.archives-ouvertes.fr/hal-01897934/log/

Putting it in web app project but I'm not sure this is the place for it.

Migrated from T1675 (view on Phabricator)

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