Set key when Explore preference is created, otherwise tapping it will cause a NPE.

BUG: 25597961

Change-Id: I1e2fc8caa961e1054472b46cbeb6aad407a1f91a

src/com/android/settings/deviceinfo/PrivateVolumeSettings.java

@@ -297,6 +297,7 @@ public class PrivateVolumeSettings extends SettingsPreferenceFragment {
     private Preference buildAction(int titleRes) {
         final Preference pref = new Preference(getPrefContext());
         pref.setTitle(titleRes);
+        pref.setKey(Integer.toString(titleRes));
         return pref;
     }