[Reimbursement] Reviewer without access edge case

I haven't tested this, but I think there may be an edge case:
- Bob creates a reimbursement report on DevHacks
- Bob assign Alice (a manager on DevHacks) as the reviewer for the report
- Bob move the report to ExpensiCon
- Alice does not have access to DevHacks and thus can't review

In this case, we should probably just clear the reviewer field, but pls first test to see whether this is a real bug or not

Start by locating the reimbursement report code that assigns reviewers and checks organization access. Reproduce the DevHacks-to-ExpensiCon scenario described in the issue to confirm whether Alice can still review. Done means the behavior is confirmed or disproved and, if it is a bug, the reviewer is cleared with a regression test.

Written by the indexing model from the issue text.