Make sure grouped term exists before using it as an object.

Fixes Trying to get property of non-object in… PHP notice.
More PHP notice/warnings data validation

Fixes PHP Notice: Undefined offset: X
Fix styling issue for add-ons list

Min-height wasn't enough for some extension descriptions. Seen here: http://cld.wthms.co/7ypt
Merge pull request #3918 from scottbasgaard/master

Make sure grouped term exists before using it as an object.