Fix bug where comment field could be missing for messed up html

Description

Closes issues: LA-1461 Related issues:

If the HTML content in a comment field was messed up (in this case, it had a <!-- comment -->), the wysiwyg editor would enter a state where all it's elements were hidden, effectively hiding the whole comment.

This fixes the problem in two places:

• Improves the detection of what constitutes an empty comment
• Make sure that the editor doesn't enter an invalid state

Notes to reviewer

Tested on user reported data, fixes issue.

Type of change

Application (affects UI or general functionality):

• New feature
• Bug fix
• Improvement

Ops / admin / CI related only (not impacting users):

• New feature
• Bug fix
• Improvement

Tests

General

• Tests have been added that prove my fix is effective or that my feature works
• Related tests have been modified/removed

Hypothesis testing:

• Soak testing has been done
• Distribution between positive / negative cases has been checked

Database

• Includes changes to database schema
• Includes necessary database migrations

Configuration

• Includes changes to configuration
• Includes configuration migration instructions in documentation

Merge checklist

• Self-review of code performed
• Feature review against specification (if applicable)
• Need for documentation has been evaluated and, if necessary, updated
• Code and implementation is reviewed by other core developer (all changes, inc. changes based on initial review)