Scroll to the last comment I made and edit it.

Pressing up in an empty comment box will edit your last comment. 

Also now when you click edit on a comment it will put the cursor at the end.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15267

![scrollup](/uploads/b056fdc479d39311f2be412458028a83/scrollup.gif)

See merge request !3757