When a comment box was open, clicking a new line to add another comment would 

discard the current comment without warning or prompting the user to save 

changes. The old comment box was silently closed, and a new one was opened.
This change warns the user before the old comment box is closed. Pressing 

cancel keeps the old comment box open. Pressing OK closes the old comment 

box without saving it, and creates a new one.

Unit tests pass.
Manually tested clicking a new line to add a comment, when a current comment 

box was open. Manually tested clicking a new line to add a comment, when a 

previously saved comment box was open. Pressing OK continues to create a 

new comment, discarding the unsaved comment. Pressing cancel returns to 

the current open comment box.