Defend against overlapping items in the workspace.

Should the Launcher's database become corrupted by
mysterious forces (e.g.: third-party launchers; botched
upgrades; smoke monsters) in such a way as to cause two
items to share the same cell, we now ignore loading the
latter.

Prevents a runtime crash (http://b/2655516).

Bug: 2655516
Change-Id: Ia514746f04f0e51b2cd07e9290589a6eab75bdd2
3 files changed