Null check if renderer is null

Local colors are added before the renderer is created which is causing
crash

Fixes: 203613925
Test: switch to user back and forward
Change-Id: I2f169434e1cb0e692045050e255d24d1f8fa7c47

packages/SystemUI/src/com/android/systemui/ImageWallpaper.java

@@ -238,9 +238,7 @@ public class ImageWallpaper extends WallpaperService {
                 Bitmap bitmap = mMiniBitmap;
                 if (bitmap == null) {
                     mLocalColorsToAdd.addAll(regions);
-                    mRenderer.use(b -> {
-                        updateMiniBitmapAndNotify(b);
-                    });
+                    if (mRenderer != null) mRenderer.use(this::updateMiniBitmapAndNotify);
                 } else {
                     computeAndNotifyLocalColors(regions, bitmap);
                 }