Cancelling the insertion of a code block still performs the insert in Safari. (BB-15855)

Summary

When writing a comment, the cancellation of the insertion of a code block fails to actually cancel that action.

Steps to Reproduce

1. Begin to add a comment
2. In the formatting bar, click the 'Code' button
3. Click 'Cancel'
4. Notice the code block is still inserted in the comment

Affects

OS X 10.11.2 (15C50)
Safari 9.0.2 (11601.3.9)