[cv] panic if UpdateCLTask.Requester is unspecified
[cv] panic if UpdateCLTask.Requester is unspecified

Bug: 1358208
Change-Id: Ib3b9691379ec105d60d03af68a19d274f963abb3
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3972457
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Auto-Submit: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>

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