Viewing a blog with no comments, but comments enabled gives undefined StdClass->commentcount error

[Andrew Nicols]

On fresh install on master using linux:

Viewing a blog as a view artefact doesn't get comment counts correctly.

Steps to reproduce:
* Create blog post with comments enabled.
* Add recent blog posts to profile view
* Create second user.
* View first user.
* View the blog as a whole - e.g. http://mahara.local/view/artefact.php?artefact=4&view=4

artefact/blog/lib.php::ArtefactTypeBlogPost->get_posts() should get comment counts but doesn't because $viewoptions['countcomments'] is empty even though the individual blog post has comments enabled.

Error message pasted to gisthub http://gist.github.com/588081