Merge "Skip null surface when validating transition" into udc-dev

        mController.mStateValidators.add(() -> {

            for (int i = mTargets.size() - 1; i >= 0; --i) {

                final ChangeInfo change = mTargets.get(i);

                if (!change.mContainer.isVisibleRequested()) continue;

                if (!change.mContainer.isVisibleRequested()

                        || change.mContainer.mSurfaceControl == null) {

                    continue;

                }

                Slog.e(TAG, "Force show for visible " + change.mContainer

                        + " which may be hidden by transition unexpectedly");

                change.mContainer.getSyncTransaction().show(change.mContainer.mSurfaceControl);