Avoid repositioning unattached overlay views

Adding a view to an overlay usually entails removing the
view from its current parent, if it has one. ViewOverlay.add() will
do this automatically. At the same time, it will check to see whether
the parent view is in a different global location than the overlay's
host view, and will adjust the added view accordingly. This enables
the caller to simply toss a view into an overlay and have it end up
at the same global position on the screen.

the problem is that the current code doesn't bother to check whether
the old parent is attached. If that parent has been removed from the
view hierarchy before this overlay operation, then it will show up as
being at (0,0) in the window, not its old location. This results in the
view being mis-positioned in the overaly.

Fix is simple: if the view's old parent is not attached, simply remove
it from that parent before adding it to the overlay; don't try to compensate
for its position which is based on wrong information.

Issue #8620319 Overlay should only use relative window locations for onscreen parents

Change-Id: I414038a6c355dfd58f9766b007ac44d535ef1889