With the change to "Create Review" in the new unified banner, we made it

much easier to have an empty review get published. It used to be that

closing the review dialog with an empty review would delete the draft,

but we now keep it around.
This change adds a validation step for review publishing to ensure that

the review is not empty.

Attempted to publish an empty review from both the unified banner and

  the review dialog. Saw the expected error message.
Ran Python and JS unit tests.