Clear WidgetCell#mItem before recylcing a WidgetCell

This fixes a bug which reuses a previous widget item spans to
compute the preview size.

Fix: 193133048
Test: manual
Change-Id: I5459882e258dc010898854dbbe52a6fa8d84796c
(cherry picked from commit 3d27207ff6ff951add0a21b699761126d1af11ec)
1 file changed