Saving a review comment without changing review state gives an error

[LDSamson]

Steps to reproduce the problem:

• Run the test application in development mode (golem::run_dev())
• Browse to subject BEL_04_772 and page CBC Regular
• Add a comment in the reviewing pane (top left), and click Save

The following error will show up:

Not a critical error, but it is confusing: the save button should not be activated for only a comment. It should only be activated when changing the review state (e.g. the form is not yet reviewed, but the check box is set to 'Reviewed'.