[logdog] Fix viewerURL on missing logs.
[logdog] Fix viewerURL on missing logs.

R=tandrii@chromium.org, 9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug: 1061187
Change-Id: I229e6f74f15e7614b9b8fe7b96963bb56fe07968
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2129192
Auto-Submit: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go