Check device for config_enableWallpaperService before calling service.

On some devices, it is possible that config_enableWallpaperService is
false, in which then there is no wallpaper service on device. Calling
WallpaperManager#getWallpaperId will then result in an NPE. We should
just do a check and return false.

Bug: 62387789
Test: RoboSettingsTest
Change-Id: I31db6845f06533d92140bf91d0f7fc7e7bedc5c5

src/com/android/settings/wallpaper/WallpaperSuggestionActivity.java

@@ -59,7 +59,8 @@ public class WallpaperSuggestionActivity extends Activity {
     @VisibleForTesting
     public static boolean isSuggestionComplete(Context context) {
         final WallpaperManagerWrapper manager = new WallpaperManagerWrapper(context);
-        return manager.getWallpaperId(WallpaperManager.FLAG_SYSTEM) > 0;
+        return manager.isWallpaperServiceEnabled() ? manager.getWallpaperId(
+                WallpaperManager.FLAG_SYSTEM) > 0 : false;
     }
 
 }

src/com/android/settings/wrapper/WallpaperManagerWrapper.java

@@ -22,12 +22,23 @@ import android.content.Context;
 public class WallpaperManagerWrapper {
 
     private final WallpaperManager mWallpaperManager;
+    private final boolean mWallpaperServiceEnabled;
 
     public WallpaperManagerWrapper(Context context) {
-        mWallpaperManager = (WallpaperManager) context.getSystemService(Context.WALLPAPER_SERVICE);
+        mWallpaperServiceEnabled = context.getResources().getBoolean(
+                com.android.internal.R.bool.config_enableWallpaperService);
+        mWallpaperManager = mWallpaperServiceEnabled ? (WallpaperManager) context.getSystemService(
+                Context.WALLPAPER_SERVICE) : null;
+    }
+
+    public boolean isWallpaperServiceEnabled() {
+        return mWallpaperServiceEnabled;
     }
 
     public int getWallpaperId(int which) {
+        if (!mWallpaperServiceEnabled) {
+            throw new RuntimeException("This device does not have wallpaper service enabled.");
+        }
         return mWallpaperManager.getWallpaperId(which);
     }
 }