Commenting on MR diff doesn't work sometimes
Summary
It looks like under some unknown conditions, commenting on MR diffs doesn't work. This is intermittent error, and I wasn't able to find reproducible process for that.
Adding comment results in error:
application-9d7ddc5….js:490 Uncaught TypeError: Cannot read property 'destroy' of undefined
Notification about comment is sent, but comment is not visible in discussion.
Steps to reproduce
Comment on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4024#note_12008228
Reproduced by @alfredo1.
/cc @jschatz1