Fixed bug allowing a request to be published with empty summary fields.

In the publish request page, if you filled the summary or description field then
deleted the contents, the fields would not be updated but the ReviewRequest
object would be updated.  This allowed a request to be published with empty
fields although the page showed they were not empty.

The fields are now emptied to then be filled with the new contents, avoiding
this issue.

Testing done: Checked in browser that the summary and description fields are
updated if you empty the field.  The Web UI does not allow the request to be
published after the field is emptied.

Reviewed at http://reviews.reviewboard.org/r/3760/
Fixes bug 2870.