Fix NPE after Exp[15]Adapter's simple constructor.

The `ExpandableListItemAdapter.<init>(Context, List<T>)` constructor fails to
initialize the `mExpandedViews` field, causing the adapter to throw an NPE 
when you first fold an item closed.

A work-around while using 2.5.2 is to use the constructor that takes three
resId's in addition to the `Context` and the array, but you need to know to
use 0, 10000 and 10001, respectively, or it'll NPE elsewhere.