Check campaigns is loaded before reading the campaign.

This cl checks if the campaigns loading is completed before fetching it. It also prevents subscribing to instant registry more than once.

Bug: b/331051412, b/331045249
Change-Id: Ib3f10d6c70137a8c9145a9c2fe0d065bbffcc986
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406314


Reviewed-by: Li Lin <llin@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: Thu Huong Vu <thv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281546}