GridLayoutManager: fix bug if current focus is on top of grid view

When focused search widget is on top of grid view and inside padding area,
FocusFinder gives gridview a negative score since its top edge
is above top edge of search widget.  So nothing happens when
click DOWN from search widget.

BrowseFragment does not have the problem since it has a customized view 
overrides focusSearch(),  but for user who is using RowsFragment directly, we
should make the default focus search working.

Change-Id: I916d9666076cb977296617075dc0721857d9a04e
1 file changed