Pull requests fail to load after git reclaims objects required for the PRs diffs (BB-7238)

We are getting an error "Something has gone terribly wrong..." on a PR. The diff starts loading (flash of rendering content) then just ends up with the oops message.

https://bitbucket.org/atlassian/aui/pull-request/234/issue-aui-1297-sortable-table-addition-for

We end up having to abandon the PR and all tracking/commenting info and doing a new one; which is a pain in the arse.