GuidedStepFragment: Fix addAsRoot restoring bug

Dont re-add root fragment when savedInstanceState can restore
them.

Bug 27972030

Change-Id: I427f171164f60b901c328f17a51349045f04eb50
diff --git a/samples/SupportLeanbackShowcase/app/src/main/java/android/support/v17/leanback/supportleanbackshowcase/app/dialog/DialogExampleActivity.java b/samples/SupportLeanbackShowcase/app/src/main/java/android/support/v17/leanback/supportleanbackshowcase/app/dialog/DialogExampleActivity.java
index 55f7575..0c71739 100644
--- a/samples/SupportLeanbackShowcase/app/src/main/java/android/support/v17/leanback/supportleanbackshowcase/app/dialog/DialogExampleActivity.java
+++ b/samples/SupportLeanbackShowcase/app/src/main/java/android/support/v17/leanback/supportleanbackshowcase/app/dialog/DialogExampleActivity.java
@@ -29,7 +29,9 @@
         super.onCreate(savedInstanceState);
         getWindow().setBackgroundDrawable(new ColorDrawable(Color.parseColor("#21272A")));
 
-        GuidedStepFragment fragment = new DialogExampleFragment();
-        GuidedStepFragment.addAsRoot(this, fragment, android.R.id.content);
+        if (savedInstanceState == null) {
+            GuidedStepFragment fragment = new DialogExampleFragment();
+            GuidedStepFragment.addAsRoot(this, fragment, android.R.id.content);
+        }
     }
 }