/browse/search/ crashes when swh-search results are not in swh-storage

swh-search is up to date with the main swh-storage cluster, while swh-web uses a replica that is currently lagging behind. This means that search results returned by swh-search may not exist in the storage.

When this happens, the JS code gets a 404 when querying https://archive.softwareheritage.org/api/1/origin/visit/latest/doc/ with an HTML body.

However, it expects to always get a JSON body, causing this crash:

https://sentry.softwareheritage.org/organizations/swh/issues/105105/?referrer=phabricator_plugin

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON
  at None (./swh/web/browse/assets/browse/origin-search.js:61:66)
  at Array.map (<anonymous>)
  at call (./swh/web/browse/assets/browse/origin-search.js:61:55)
...
(3 additional frame(s) were not displayed)

which means the page gets stuck on the "Checking" spinner

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Migrated from T4675 (view on Phabricator)