Add tests for BP_Groups_Group::get_group_extras()

See #5416

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7938 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Don't query for group extras if user is not logged in

Saves a couple needless database queries for unauthenticated users.

Fixes #5416

Props lenasterg for initial patch

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7939 cdf35c40-ae34-48e0-9cc9-0c9da1808c22