Fix a crash on Permission Denied in the Review General Comment API.
Review Request #11052 — Created June 22, 2020 and submitted
When trying to POST to the Review General Comment API without permission
to modify the review, the API would pass to the wrong variable to
get_no_access_error(), causing an HTTP 500.
This is a simple change that fixes the variable and adds a unit test to
ensure the fix does not regress.
Unit tests pass.