IMS-VT: Call showAnswerUi when onUpgradetoVideo callback is called

- Glowpad wrapper is now seen when we receive an upgrade request as
  showAnswerUi is called when onUpgradeToVideo callback is invoked

- Without this change, we don't see the Glowpad wrapper

BUG=28384174
Change-Id: Ibeb1a49f6cc9b8b0d70d167debf496f897c7c14f
diff --git a/InCallUI/src/com/android/incallui/AnswerPresenter.java b/InCallUI/src/com/android/incallui/AnswerPresenter.java
index 6757268..883b54f 100644
--- a/InCallUI/src/com/android/incallui/AnswerPresenter.java
+++ b/InCallUI/src/com/android/incallui/AnswerPresenter.java
@@ -128,10 +128,7 @@
     @Override
     public void onUpgradeToVideo(Call call) {
         Log.d(this, "onUpgradeToVideo: " + this + " call=" + call);
-        if (getUi() == null) {
-            Log.d(this, "onUpgradeToVideo ui is null");
-            return;
-        }
+        showAnswerUi(true);
         boolean isUpgradePending = isVideoUpgradePending(call);
         InCallPresenter inCallPresenter = InCallPresenter.getInstance();
         if (isUpgradePending