If nothing to animate, don't call remote animator

Otherwise we'll end up with weird transitions when just switching
focus because focus switch causes an app transition to run.

Test: go/wm-smoke
Test: Enter PIP, click on PIP window, click on launcher window
to execute an empty app transition.

Change-Id: Ie42ad808ff4d4646570c122fd3b964e3255a57bc
diff --git a/services/core/java/com/android/server/wm/RemoteAnimationController.java b/services/core/java/com/android/server/wm/RemoteAnimationController.java
index 8515dcb..0048983 100644
--- a/services/core/java/com/android/server/wm/RemoteAnimationController.java
+++ b/services/core/java/com/android/server/wm/RemoteAnimationController.java
@@ -88,6 +88,10 @@
      * Called when the transition is ready to be started, and all leashes have been set up.
      */
     void goodToGo() {
+        if (mPendingAnimations.isEmpty()) {
+            onAnimationFinished();
+            return;
+        }
         mHandler.postDelayed(mTimeoutRunnable, TIMEOUT_MS);
         try {
             mRemoteAnimationAdapter.getRunner().onAnimationStart(createAnimations(),