Fix gestures summary text when there is no sensor for assit.

Should exit the summary handling if sensor is not available.

Change-Id: I5918fa5ac614db48fc2c41e1de555d1ba6928bd4
Fix: 64039312
Test: make RunSettingsRoboTests

src/com/android/settings/gestures/GesturesSettingPreferenceController.java

@@ -64,6 +64,7 @@ public class GesturesSettingPreferenceController extends AbstractPreferenceContr
     public void updateState(Preference preference) {
         if (!mFeatureProvider.isSensorAvailable(mContext)) {
             preference.setSummary("");
+            return;
         }
         final ContentResolver contentResolver = mContext.getContentResolver();
         final boolean assistGestureEnabled = Settings.Secure.getInt(