R1:304467feb2ae

Stabilize fatals when a build has a build plan the viewer can't see because of policy restrictions

Summary:
Ref T13526. Currently, if a build plan is restricted, viewers may fatal when trying to view related builds.

The old behavior allowed them to see the build even if they can not see the build plan. This is sort of incoherent, but try to stabilize things before fixing this.

Test Plan:
This is a muddy change.

- Created a build with a build plan that Alice can't see.
- As Alice, viewed the build…