Expand review when jumping to comment from issue table.

When clicking on an issue in the issue table, we bring the user to the
associated comment. This wasn't working if the comment was part of a review
that had been collapsed. Now we expand the appropriate review before sending
the user to the comment.

Fixes issue #3770.
Assert that a comment is passed to CommentDialogView.

At some point before committing my CommentDialogView change, logic
leading to an assertion moved, which we needed to ensure that there was
some comment passed to CommentDialogView. The assertion is now added to
CommentDialogView.create, which first references the comment.