Correctly hide cancelled comments

There's currently a bug with adding a comment to question or an answer:
###### Steps to reproduce:

- click add comment
- click cancel button on shown editor

###### Expected result:
Form hides, no comment added

###### Actual result:
Empty comment is added to dom, then if page is refreshed it's not there anymore

This PR fixes this bug, however I'm not totally sure if it's affecting anything else.