[Sprint/PinkPanther](fix): Return error if the provided group is not found by group report. #874

Closes #874 (closed)

Summary

Noticed from Sentry, this endpoint was getting called with an invalid user.

Test

Hit http://{{host}}/api/v1/groups/review/1020865576266620928/count with an invalid group ID. (if you're on postman you can go to Ben's\ Corner/api/groups/groups\ v1\ reported)

Reproducing the bug locally

New request after fix