Correct "cropping" of widget picker's search bar

To corrent, I added 1dp of bottom margin. Not doing this, the framework
ignores the dropped shadow due to the elevation when some text is
entered in the box, leading to the observed cropping.

Fix: 186722040
Test: Manually
Change-Id: I746a8f014197552416ed9c40e9736baf22794c5f