Fix visual glitch in app transition.

When dummy animation is being used, set the alpha to 0 or 1 depending
on whether the app was previously hidden or visible.

Change-Id: I1a4e3cdb4b9ca4a6aef58e47bf26e5adbef66a7f

Author: Craig Mautner

services/java/com/android/server/wm/AppWindowAnimator.java

@@ -185,6 +185,8 @@ boolean stepAnimationLocked(long currentTime, int dw, int dh) {
                 // it as not animating for purposes of scheduling transactions;
                 // when it is really time to animate, this will be set to
                 // a real animation and the next call will execute normally.
+                hasTransformation = true;
+                transformation.setAlpha(mAppToken.reportedVisible ? 1 : 0);
                 return false;
             }