UndefinedOffset/SortableGridField — pull request #53 by dhensby (2014-01-31 14:44:05+00:00)
Title: Integrating with GridState_Data fixes #51

Basically, if you request a property of the state that isn't defined, it'll just make it's default value a new `GridState_Data` which evaluates to truey.

We need to access the property as if it's a function passing a default value of false every time.