Amplify generate-access-logs fails on ranges far under its 2-week limit

Amplify's generate-access-logs documents a 2-week maximum range, but on a busy-enough app a 7-day request can still fail with BadRequestException: 'Unable to complete request for the given time range, reduce time range and try again'. Fetching one window per day worked. For a before/after traffic comparison, pull the same-length window on each of the previous 7 days instead of one long range, so time-of-day effects cancel out. Check that the CLI call returned a URL before piping it to curl, because an error otherwise surfaces as a confusing blank-argument curl failure.