protected View getHeaderView(int position, View convertView, ViewGroup parent) {
        if (mDelegate.getNumHeaders() == 0) {
            return null;
        }

        return mDelegate.getHeaderView(translatePosition(position).mHeader, convertView, parent);
    }
Counts the number of items that would be need to fill out the last row in
the group of items with the given header.

@param header Header set of items are grouped by.
@return The count of unfilled spaces in the last row.
Library/src/com/tonicartos/widget/stickygridheaders/StickyGridHeadersBaseAdapterWrapper.java