Fix hang on rotation.

A recent optimization to only send updates to WindowManagerService
when there is something to report backfired. One bit indicating
change had negative polarity so the update should also have been
sent when this bit was cleared. This change alters the bit to
positive polarity.

Fixes bug 6780496.

Change-Id: I3336812a60534ebffc9e94b2fb1d0df4d6969bca