Comment 2 for bug 987838

The attached branch simply ensures that the screenshot view is not dependent on the redundant (and perhaps-not-set) is_latest field.

Another part of the fix for this should be ensuring that the check_all_latest command is run after each import (import_app_install_data and import_for_purchase), but I want to check with achuni about that first as it looks like the kind of command we wouldn't want to run unnecessarily (ie. after each import of a distroseries, but rather after importing all distroseries - which may be why it's been left manual).