Don't use deleted Node object in setSizeScreenWidthAndScale

The call to forceLayout may cause the Node object to be
deleted. Avoid crash by check that the Node object is
still valid when forceLayout has returned.

picked from
https://android-review.googlesource.com/#/c/17537/

Change-Id: Ia4ecd1a633b55ae3e7c9db0ca17a8f7d481eb75d