NullPointerException when launching plugin

[amchiclet]

Steps to reproduce.

1. Run a type qualifier inference in the Type Qualifier Inference eclipse instance.
2. Have either the Separated Changes View or Separated Errors View open before closing the Type Qualifier Inference eclipse instance.
3. Launch the Type Qualifier Inference eclipse instance again.
4. A NullPointerException will happen on the view that was not closed.

[amchiclet]

Fixed by 9c9c640.