Fix endless looping in layout.

An odd alignment of the stars can end up with all of mAppToken.allDrawn
animating and mAppToken.startingDisplayed all false, and animation not
null. In such a case we can continue returning false but still pass
the test in WindowAnimator.updateWindowsAndRotation setting
wasAnimating to true. The combination continually sets the
FINISH_LAYOUT_REDO_WALLPAPER bit in mPendingLayoutChanges.

Fixes bug 6304838.

Change-Id: Ie7a7b39ea218213f51dc3df3eefe4ff03f1d885d