Return colors of areas even if they are not in current page

Bug: b/189827568
Test: manual
Change-Id: I917c7b8e61cd18d04075600f4337806deb7f41bf

core/java/android/service/wallpaper/WallpaperService.java

@@ -1719,6 +1719,7 @@ public abstract class WallpaperService extends Service {
                 float finalStep = step;
                 int finalPageIndx = pageIndx;
                 Bitmap screenShot = page.getBitmap();
+                if (screenShot == null) screenShot = mLastScreenshot;
                 if (screenShot == null || screenShot.isRecycled()) {
                     if (DEBUG) {
                         Log.d(TAG, "invalid bitmap " + screenShot