Problems when restoring Ranking Window

[Mathieu Bastian]

Problems appears if Ranking Window has been closed and be reopened after new Gephi start. When restored after a project has been created or opened, its controls stays disabled. Then, if workspace is changed, it throws the following exception:

java.lang.NullPointerException
 at org.gephi.ranking.impl.RankingModelImpl$1.unselect(RankingModelImpl.java:71)
 at org.gephi.project.impl.ProjectControllerImpl.fireWorkspaceEvent(ProjectControllerImpl.java:534)
 at org.gephi.project.impl.ProjectControllerImpl.closeCurrentWorkspace(ProjectControllerImpl.java:456)
 ...

Way to reproducte:
1) Open Gephi with a graph file
2) Close Ranking window
3) Restart gephi
4) Open a graph file
5) Got to Window > Ranking
The Ranking window has disabled controls
6) Create a new workspace (Ctrl + N)
7) Switch workspace
Throw NullPointerException