Don't save every comment when publishing from the "Edit Review" dialog.
Don't save every comment when publishing from the "Edit Review" dialog.

The code that calculated whether or not we needed to save the comment models in
the "Edit Review" dialog was saving every comment, because we never fetched the
original extra data (which meant that it was comparing the extra data object
against undefined). This change adds some code to actually assign
`this._origExtraData`, which fixes the issue.

Testing done:
- Ran js-tests
- Added some instrumentation and checked that when I had modified (but not
  saved) a comment, it would save it as part of the publish operation, but if I
  hadn't modified it, or if I'd modified and saved it, it would skip that and
  only save the review.

Reviewed at https://reviews.reviewboard.org/r/6518/

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