Fixes NPE when running dumpsys wallpaper

Bug: 277077910
Test: code compiles, can't test because can't repro failure state
Change-Id: I67adf550cee51273e94b21479fdfaa3f6f252578

services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

@@ -3569,6 +3569,7 @@ public class WallpaperManagerService extends IWallpaperManager.Stub
     private void dumpWallpaper(WallpaperData wallpaper, PrintWriter pw) {
         if (wallpaper == null) {
             pw.println(" (null entry)");
+            return;
         }
         pw.print(" User "); pw.print(wallpaper.userId);
         pw.print(": id="); pw.print(wallpaper.wallpaperId);