SurfaceFlinger: Ensure syncInputWindows is processed.

Imagine the following situation:
1. We set mPendingInputWindowCommands.syncInputWindows = true, and block
   on the condition variable from a binder thread.
2. We Handle MessageQueue::INVALIDATE
3. This will invoke handleTransaction which will copy
   mPendingInputWindowCommands to mInputWindowCommands and clear
   mPendingInputWindowCommands
4. Now imagine due to the performSetActiveConfig conditional in
   MessageQueue::INVALIDATE handler we break out of our handling
   before calling updateInputFlinger.
5. Since we didn't call updateInputFlinger we will never receive
   setInputWindowsFinished and the condition variable is still blocking
6. The next time we enter MessageQueue::INVALIDATE we have already cleared
   mPendingInput WindowCommands, and so by the time we get to
   updateInputFligner we no longer think a sync is required and don't request
   the callback.
7. No callback ever arrives, our binder thread blocks for the whole 5 seconds.

To fix this we just ensure mInputWindowCommands.syncInputWindows wont become
false after becoming true until we actually are sure we will broadcast
the condition variable.

Bug: 147257069
Test: Existing tests pass
Change-Id: I5f5728c29f36bb5e0bdf11b3f34e956bb529706f