SurfaceView: Reset window stopped state when attaching to window.

We may be stopped, removed from the view hierarchy, and then only
attached again after the activity has been restarted, missing
our WindowStopped callback to set mWindowStopped=false. At this point
we are being added to a visible view, or in ViewRoot#performTraversals
so we can assume we are not stopped.

Test: Manual from bug.
Bug: 37682805
Change-Id: Idf8e061fb7f83b00992a274c7dd704f9e0fcff5f