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
diff --git a/src/com/android/launcher2/ItemInfo.java b/src/com/android/launcher2/ItemInfo.java
index ca2ea86..a96d9ae 100644
--- a/src/com/android/launcher2/ItemInfo.java
+++ b/src/com/android/launcher2/ItemInfo.java
@@ -137,4 +137,9 @@
     
     void unbind() {
     }
+
+    @Override
+    public String toString() {
+        return "Item(id=" + this.id + " type=" + this.itemType + ")";
+    }
 }