Clear the bitmap associated with canvases.

Change-Id: Ic100a51960f8c0e7d8b3a107b64d23c7d70e6da9
diff --git a/src/com/android/launcher2/IconCache.java b/src/com/android/launcher2/IconCache.java
index 2977383..20c5f34 100644
--- a/src/com/android/launcher2/IconCache.java
+++ b/src/com/android/launcher2/IconCache.java
@@ -101,6 +101,7 @@
         Canvas c = new Canvas(b);
         d.setBounds(0, 0, b.getWidth(), b.getHeight());
         d.draw(c);
+        c.setBitmap(null);
         return b;
     }