Make issue_opened and issue_status more consistent.

If a user creates a comment with an issue, and later removes that issue before
publishing, we end up in a weird state where the issue_status is still 'O' but
issue_opened is false. This change fixes it to clear out issue_status when
removing the issue_opened bit.

Testing done: Ran unit tests.
Fixes bug 2984.
Reviewed at https://reviews.reviewboard.org/r/4404/