Added null check while fetching the context URI resource

This CL aims at adding a null check before we convert the fetched URI
character sequence to string format.

Bug: b/257012915
Test: Tested by building and flashing on local, and seeing everything
works okay as expected before for 3P livewallpapers.

Change-Id: Id90367ee16d479591e524d7c2c5774ec3c483628

core/java/android/app/WallpaperInfo.java

@@ -292,12 +292,12 @@ public final class WallpaperInfo implements Parcelable {
             packageName = mService.serviceInfo.packageName;
             applicationInfo = mService.serviceInfo.applicationInfo;
         }
-        String contextUriString = pm.getText(
-                packageName, mContextUriResource, applicationInfo).toString();
-        if (contextUriString == null) {
+        CharSequence contextUriCharSequence = pm.getText(
+                packageName, mContextUriResource, applicationInfo);
+        if (contextUriCharSequence == null) {
             return null;
         }
-        return Uri.parse(contextUriString);
+        return Uri.parse(contextUriCharSequence.toString());
     }
 
     /**