smartlist: move placeholder to center in tablet layout

Change-Id: Iab8050df9887539f9bcc2fce333ba99f4f910069
diff --git a/ring-android/app/src/main/res/layout-w720dp-land/frag_smartlist.xml b/ring-android/app/src/main/res/layout-w720dp-land/frag_smartlist.xml
index cca5f76..8cf4ad5 100644
--- a/ring-android/app/src/main/res/layout-w720dp-land/frag_smartlist.xml
+++ b/ring-android/app/src/main/res/layout-w720dp-land/frag_smartlist.xml
@@ -13,10 +13,9 @@
         android:layout_height="match_parent"
         android:layout_marginTop="?actionBarSize">
 
-        <LinearLayout
+        <FrameLayout
             android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:orientation="vertical" >
+            android:layout_height="match_parent" >
 
             <LinearLayout
                 android:id="@+id/placeholder"
@@ -62,7 +61,7 @@
                 tools:listitem="@layout/item_smartlist"
                 android:layout_marginBottom="@dimen/navigation_bottom_height"/>
 
-        </LinearLayout>
+        </FrameLayout>
 
         <com.google.android.material.floatingactionbutton.ExtendedFloatingActionButton
             style="@style/Widget.AppTheme.MainActionButton"