Catch exception when getting PermissionControllerManager in PolicyService

There's a possible race condition when a user is being removed, where we
may try to create a PermissionControllerManager for a user that's no
longer valid. If that happens, handle the exception gracefully

Fixes: 302466721
Test: presubmit
Change-Id: If007f1320c445a29e0d3738275c5716a67bca0d9