[resource] avoid derived state calculation when unloading a resource
https://bugs.eclipse.org/bugs/show_bug.cgi?id=451668

Change-Id: Iaeb72a17f57884b8c63e1fb5a6e81e9a04ec34e7
Signed-off-by: Dennis Huebner <dennis.huebner@itemis.de>
[releng] Further changes needed for EMF 2.11 nightly