gs-loading-page: Update software cache on first run

Currently, the software cache is only updated on startup if it’s empty. However, this is not helpful in situations where the cache is present but very old when gnome-software is first started. This can happen on machines shipped with Endless OS (which pre-seeds the software cache) which have sat in storage for a while before being booted for the first time by their user. In that situation, old apps would be shown, which is confusing and not a good user experience.

As a compromise, update the app cache if it’s older than 24h when gnome-software is first started. On subsequent starts, revert to the old behaviour of only updating the cache if it’s missing.

Signed-off-by: Philip Withnall withnall@endlessm.com