Make sure we initialize to enable the default voice interaction service.

We weren't taking care of the case of an upgrade to L.  The main
change here is that the voice interaction service setting now has
an empty string when the user has explicitly said they don't want
one, so when it is null we will initialize it to its default.

Change-Id: Icdd30b4f09498f8928cea759a64628bd43bc5d0e
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 8886559..b4fa972 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -2331,7 +2331,7 @@
          * preference, this rotation value will be used. Must be one of the
          * {@link android.view.Surface#ROTATION_0 Surface rotation constants}.
          *
-         * @see Display#getRotation
+         * @see android.view.Display#getRotation
          */
         public static final String USER_ROTATION = "user_rotation";
 
@@ -2439,7 +2439,8 @@
         public static final String SHOW_TOUCHES = "show_touches";
 
         /**
-         * Log raw orientation data from {@link WindowOrientationListener} for use with the
+         * Log raw orientation data from
+         * {@link com.android.internal.policy.impl.WindowOrientationListener} for use with the
          * orientationplot.py tool.
          * 0 = no
          * 1 = yes