isolate: fix query duration finding older ContentEntry
isolate: fix query duration finding older ContentEntry

Currently query can fail to find older ContentEntry.

Bug: 1004389
Change-Id: Idbab5ca0457851b55e9b50cc97b5ac131dc5454e
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1923468
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py