[logdog] Fix another likely leak in butler.
[logdog] Fix another likely leak in butler.

R=9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug: 939368
Change-Id: I502acdb881e5d6925b5146735be37d62d3f7897b
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1755511
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