There were some obscure cases where users could trigger negative

counters in the dashboard for review requests. These have been hard to

track down, but with enough bugs opened, we had a somewhat decent

starting point for some of these.
What all the repro cases had in common was that a review request was, at

some point, discarded. In most other cases, a review request was also

permanently deleted.
Through some digging, I found there were a couple cases where you could

trigger these negative counters:
1) Closing a review request twice with two different statuses (through

   the API or by opening a review request in two tabs and closing as

   Submitted in one, Discarded in another).
2) Permanently deleting a closed (discarded or submitted) review

   request.
What these had in common is that they were decrementing counts when not

coming from a PENDING_REVIEW state.
This change tightens the code to only decrement when we were in this

state. It also cleans up a lot of the code by moving all the

incrementing and decrementing logic into reusable functions, so that we

never become inconsistent between them.
Unit tests were added to check these new states. Additional tests were

added for other conditions I could think of (which passed anyway, but it

doesn't hurt to beef up the test suite).
I also was able to simplify and strengthen these tests by moving all the

count assertions into a utility function that would guarantee all

possible values were checked. This helped to improve readability,

maintainability, and consistency between the tests.
This change will be backported to release-1.7.x.

The new unit tests failed with -1 values without the fixes to the counter

updates. After the fixes, all tests passed.
I also verified the failures by hand, and verified they've been fixed.