Clear bitmap from canvas after done drawing to it.

Change-Id: I0ebc8510021a2dd0b147ced7890d939ec47809f6
diff --git a/src/com/android/browser/WallpaperHandler.java b/src/com/android/browser/WallpaperHandler.java
index cd896da..6437b1a 100644
--- a/src/com/android/browser/WallpaperHandler.java
+++ b/src/com/android/browser/WallpaperHandler.java
@@ -162,6 +162,7 @@
             Canvas canvas = new Canvas(bm);
             oldWallpaper.setBounds(0, 0, width, height);
             oldWallpaper.draw(canvas);
+            canvas.setBitmap(null);
             try {
                 wm.setBitmap(bm);
             } catch (IOException e) {