Check FaceManager before get system service

Bug: 136788181
Test: adb shell am start -a android.settings.FACE_SETTINGS is not
      crashed

Change-Id: If727ab4aa3b4043fa2e4e8c13392e32d566b1bbb
diff --git a/src/com/android/settings/biometrics/face/FaceSettings.java b/src/com/android/settings/biometrics/face/FaceSettings.java
index ba1aa1d..79198c5 100644
--- a/src/com/android/settings/biometrics/face/FaceSettings.java
+++ b/src/com/android/settings/biometrics/face/FaceSettings.java
@@ -114,16 +114,16 @@
         super.onCreate(savedInstanceState);
 
         final Context context = getPrefContext();
-        mUserManager = context.getSystemService(UserManager.class);
-        mFaceManager = context.getSystemService(FaceManager.class);
-        mToken = getIntent().getByteArrayExtra(KEY_TOKEN);
-
         if (!isAvailable(context)) {
             Log.w(TAG, "no faceManager, finish this");
             finish();
             return;
         }
 
+        mUserManager = context.getSystemService(UserManager.class);
+        mFaceManager = context.getSystemService(FaceManager.class);
+        mToken = getIntent().getByteArrayExtra(KEY_TOKEN);
+
         mUserId = getActivity().getIntent().getIntExtra(
                 Intent.EXTRA_USER_ID, UserHandle.myUserId());